- Email: [email protected]
Micro-PIXE analysis of strontium in Arctic char, Salvelinus alpinus, otoliths from Quttinirpaaq National Park, Nunavut, Canada
Nuclear Instruments and Methods in Physics Research B 189 (2002) 190–195 www.elsevier.com/locate/nimb
Micro-PIXE analysis of strontium in Arctic char, Salvelinus alpinus, otoliths from Quttinirpaaq National Park, Nunavut, Canada J.A. Babaluk
a,*
, J.L. Campbell b, C.L. Evans a, N.M. Halden c, S.R. Mejia c, Z. Nejedly b, J.D. Reist a, W.J. Teesdale b
a
Fisheries and Oceans Canada, 501 University Crescent, Winnipeg, Manitoba, Canada R3T 2N6 Guelph-Waterloo Physics Institute, University of Guelph, Guelph, Ontario, Canada N1G 2W1 Department of Geological Sciences, University of Manitoba, Winnipeg, Manitoba, Canada R3T 2N2 b
c
Abstract Arctic char, Salvelinus alpinus, exhibit either lake resident or anadromous (sea-run) life histories. Anadromy is less prevalent at the northern and southern extremes of the distribution. Effective conservation and management of char requires knowledge of life histories exhibited by individuals and populations. Micro-PIXE line-scans were used to determine the distribution of strontium (Sr) in otoliths from which life history patterns were determined for Arctic char from 10 lakes in Quttinirpaaq National Park in the Canadian High Arctic. Although most populations were lake resident as expected, the data indicated that a component of the char population from one lake was anadromous. This represents the most northerly known char population to exhibit anadromy. Mean Sr concentrations in otoliths of char from all populations, as determined by point analysis and also from line-scan data, showed no significant differences between the methods. Mean Sr concentrations (from point analysis) showed significant differences between some of the populations. These differences combined with other analyses (e.g. morphometrics, genetics) can be used to differentiate biological populations. Thus, micro-PIXE analysis is a useful tool for assessing diversity in Arctic char and contributing to their management and conservation in the park. Ó 2002 Elsevier Science B.V. All rights reserved. PACS: 32.30.Rj; 82.80.Ej Keywords: PIXE; Proton microprobe; Fish; Otolith; Anadromy; Stock discrimination
1. Introduction A basic understanding of the biology and diversity of Arctic char, Salvelinus alpinus, popu-
*
Corresponding author. Tel.: +1-204-983-5143; fax: +1-204984-2403. E-mail address: [email protected] (J.A. Babaluk).
lations in Quttinirpaaq National Park is fundamental to Parks Canada’s long-term conservation and management plans for these fish [1]. Although Arctic char is the only freshwater fish species in the Canadian High Arctic including Quttinirpaaq National Park [2], the species exhibits great diversity at a number of levels below that of species. This includes: (a) life history type (e.g. anadromous or non-anadromous, i.e. sea-run or not),
0168-583X/02/$ - see front matter Ó 2002 Elsevier Science B.V. All rights reserved. PII: S 0 1 6 8 - 5 8 3 X ( 0 1 ) 0 1 0 4 0 - 0
J.A. Babaluk et al. / Nucl. Instr. and Meth. in Phys. Res. B 189 (2002) 190–195
191
(b) ecological type (e.g. pelagic or benthic forms), (c) trophic type (e.g. planktivore or piscivore), (d) evolutionary lineages (e.g. subspecies, biological stocks), as well as, (e) variants within many of the above types (e.g. life history variability). This diversity can be observed through a number of techniques, but is best understood and accomplished by using several complementary approaches such as: (a) morphology (e.g. body form and function), (b) genetics (e.g. delineation of groups using DNA chemistry), (c) otolith microchemistry (e.g. life history types, stocks), (d) stable isotopes and diet (e.g. trophic pattern) and (e) population dynamics (e.g. age and size structure). Otoliths (‘‘ear stones’’) are small, paired structures found in a fish’s inner ear that are used mainly to detect orientation and acceleration. They are composed mainly of a calcium carbonate (aragonite) and protein matrix; but trace elements similar to calcium (Ca), such as strontium (Sr), can be incorporated into or replace Ca in the otolith [3]. The Ca and trace elements are derived mainly from the waters that the fish inhabits [4,5]. Otoliths do not undergo resorption during the life of the fish [4]. Sea water contains, on average, 8.0 mg l1 Sr whereas freshwater contains 0.1 mg l1 Sr [6]. These differences in Sr concentrations are reflected in otolith composition. We have previously shown that they can retrospectively indicate anadromous behaviour [7] and can provide details regarding the habitats occupied early in a fish’s life [8]. A previous micro-PIXE study of Lake Hazen char otolith Sr distribution determined that both large and small forms of Lake Hazen char [9] were non-anadromous [10]. As part of an ongoing study of char ecology in the Quttinirpaaq National Park, we extended the otolith microchemistry study to: (a) determine the extent of anadromy (if any) existing within park char populations and (b) provide additional trace element, in particular Sr, information to assist in discriminating stocks or populations.
the northern end of Ellesmere Island, Nunavut (Fig. 1). The park, with an area of 37 775 km2 , is the second largest national park in Canada. There are relatively few lakes in the park and while most of these lakes provide suitable habitat for some aquatic flora and invertebrates, most are too shallow to support populations of Arctic char [1]. Our study was confined to lakes with known char populations in the area around Lake Hazen, the largest lake (540 km2 ) within the park and also the largest lake in the Canadian Arctic located completely north of the Arctic Circle. Otoliths were collected from Arctic char from 10 lakes in Quttinirpaaq National Park (Fig. 1): Lake A, Alexandra Lake, Lake B, Craig Lake, Ekblaw Lake, Lake Hazen, Heintzelman Lake, Kilbourne Lake, Lewis Lake and Murray Lake. One otolith from each of 10 char from each lake, except Lake Hazen (n ¼ 48) and Craig Lake (n ¼ 9), was prepared for micro-PIXE analysis [10]. The proton beam of the University of Guelph proton microprobe entered the otolith surface at a 45° angle. Beam energy was 3 MeV, diameter was 5–10 lm and current was approximately 5 nA. The excitation volume was approximately 30 lm in depth. The beam caused no apparent damage to the otoliths. One line-scan of Sr and other trace elements, such as zinc, K X-ray intensity for each otolith was obtained by rastering the proton beam along a transect from the core area to the dorsal edge of the otolith incorporating all yearly deposits (i.e. annuli). Three, and in some cases six, point analyses for each fish were conducted in the core area of each otolith (i.e. within the first annulus). For comparison with Sr concentrations derived from point analyses, core area Sr was also assessed by calculating the mean Sr value from the first 50 lm of the line-scan (mean of approximately 12 values for each otolith). Detection limit for Sr was 1–2 ppm. Further details on proton microprobe procedures are given in previous publications [11,12].
2. Study area, sample collection and methodology
3. Life history determination
Quttinirpaaq National Park (formerly Ellesmere Island National Park Reserve) is located at
Scanning proton microprobe transects across otoliths of known non-anadromous Arctic char in
192
J.A. Babaluk et al. / Nucl. Instr. and Meth. in Phys. Res. B 189 (2002) 190–195
Fig. 1. Map of the Lake Hazen area, Quttinirpaaq National Park showing collection locations and dates.
other areas of the Canadian Arctic and both large and small forms of Lake Hazen char showed a relatively constant and low Sr content (a ‘‘flat’’ Sr profile) from the core area to the outer edge of the otolith [10]. This suggested that these fish spent their entire life in an environment in which the Sr content was relatively constant and low (i.e. freshwater). Although Lake Hazen char have access to the sea via the Ruggles River, line-scans showed no evidence for anadromous behaviour [10; this study]. It appears that due to its length (approximately 29 km) and velocity (up to 2.25 m s1 ), the Ruggles River acts as an effective migration barrier to Lake Hazen char [13]. As expected, all char analysed from Quttinirpaaq National Park with no access (or no direct access) to the sea (Lake A, Lake B, Craig Lake, Ekblaw Lake, Kilbourne Lake and Lewis Lake) showed similar freshwater resident Sr profiles. Fig. 2 is representative of a typical Sr profile obtained from an otolith of a known non-anadromous char from one of these lakes. Although Alexandra and Murray lakes have direct outlets to the sea (Fig. 1),
Fig. 2. Typical Sr profile from a scanning proton microprobe line-scan of an otolith from a known non-anadromous Arctic char from Lake A.
all Sr line-scans from these lakes indicated only non-anadromous behaviour. An insurmountable waterfall and an extremely steep gradient prevents two-way passage of char along the outlet rivers from Murray and Alexandra lakes, respectively.
J.A. Babaluk et al. / Nucl. Instr. and Meth. in Phys. Res. B 189 (2002) 190–195
Heintzelman Lake also has direct access to the sea (Fig. 1). Nine of 10 char analysed from here exhibited typical freshwater Sr profiles (Fig. 3(a)). However, one showed a profile similar to those of known anadromous char from other areas of the Canadian Arctic (Fig. 3(b)). The pattern of Sr distribution for this 11-year-old fish had a low Sr region corresponding to the core area (within the first annulus) and the first several annuli. This region was similar to that observed for the whole otolith transect in known non-anadromous char (see Fig. 2). A marked increase in Sr corresponds to the fifth annulus, indicating that in its sixth year of life, this fish migrated to the sea; a decline in Sr within the same year (annulus) indicated that the fish returned to freshwater to over-winter. The three Sr peaks indicated that this char migrated between fresh and sea water in three consecutive years (i.e. years 6, 7 and 8). For the remaining three years of its life, it remained in freshwater. This behaviour is slightly different than most other anadromous char populations in the Canadian Arctic; most anadromous char exhibit annual migratory behaviour once they migrate to the sea for the first time [14]. The Heintzelman Lake char appears to be an example of a fish with facultative anadromous behaviour (i.e. the fish may migrate only when environmental conditions are favour-
193
able or when energetic constraints compel it to do so). More otoliths from Heintzelman Lake char will be collected and analysed to further study the anadromous behaviour regimen of this population. Based on our otolith micro-PIXE work, we suggest that the Heintzelman Lake (81°420 N, Fig. 1) char population is currently the most northern known population to exhibit anadromous behaviour. A search of pertinent literature found no reports of anadromous char at higher latitudes. However, there are several lakes further north on Ellesmere Island (within and outside the park) and also may be some in Greenland with outlets to the sea that may contain anadromous char populations. Our micro-PIXE study of char otoliths will continue as samples from these lakes are collected.
4. Stock discrimination Variation between the two methods for determining otolith core Sr (line-scan and point analyses) and between lake (population) differences is shown in Fig. 4. There were no significant differences between means for the two methods for each lake (paired t-tests). Thus, either method is suitable for determining otolith core Sr in Arctic char. Subsequent retrospective life history studies using
Fig. 3. Representative Sr profiles from scanning proton microprobe line-scans of otoliths (superimposed on optical images of the otoliths) from (a) a non-anadromous Heintzelman Lake Arctic char and (b) an anadromous Heintzelman Lake char. Annuli (age) are indicated by numbered triangles.
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J.A. Babaluk et al. / Nucl. Instr. and Meth. in Phys. Res. B 189 (2002) 190–195
Fig. 4. Differences in mean Sr concentrations (1 standard deviation) in otolith core areas of Arctic char summarized between methods and lakes of Quttinirpaaq National Park (dots ¼ means derived from point analysis; open circles ¼ means from line-scans).
line-scans will have the added benefit of additional information for stock discrimination also being readily available. For studies that are concerned with stock discrimination only, point analysis is a more efficient method of gathering the information. Less microprobe time is required (each point analysis takes about 5 min to collect the data, whereas a typical line-scan of an Arctic char otolith requires approximately 25 min). As there were no significant differences between the two methods of determining otolith core Sr, we compared population (lake) differences by performing an analysis of variance of means derived
by point analysis. There were significant differences between Sr means for some of the lakes (Fig. 5). There were indications of at least three distinctly different groups of char in Quttinirpaaq National Park lakes: (1) Craig Lake char were significantly different from all other char except those from Lewis Lake; (2) Alexandra and Murray lakes char were not significantly different from each other but were different from all other lakes; and (3) the remaining group of lakes. Within this latter group, there were some with significant differences as well as pairs of lakes with no differences in otolith Sr concentrations. The differences in Sr concentrations might reflect differences in water Sr concentrations [4] and thus ultimately differing geology in the area. However, such variability may also result from differences in foraging activities by different forms of char within the lakes [15] and may be attributable in part to variability in char life history and small sample sizes used in our analyses. Analyses of additional fish from these locations and relating results from otolith microchemistry to local geology, and morphology and form should resolve this.
5. Conclusions Micro-PIXE analysis of Sr in Arctic char otoliths provides biologically relevant information. Mean Sr concentrations in otolith cores, as determined by point and line-scan analyses, showed no
Fig. 5. Levels of significance between pairs of lakes from analysis of variance of mean otolith core Sr concentrations as determined by point analysis (N.S.: non-significance; *: p < 0:05).
J.A. Babaluk et al. / Nucl. Instr. and Meth. in Phys. Res. B 189 (2002) 190–195
significant differences between the methods so either can be used depending on the objectives of the study. Micro-PIXE analysis of otolith Sr can retrospectively determine and assess life histories and when used with other techniques (e.g. genetics, morphology) can contribute to discrimination of stocks.
Acknowledgements This work was funded by Parks Canada and Fisheries and Oceans Canada with additional support from Natural Resources Canada (Polar Continental Shelf Project) and the Natural Sciences and Engineering Research Council of Canada.
References [1] Parks Canada, Ellesmere Island National Park Reserve Resource Description and Analysis, Department of Canadian Heritage, Winnipeg, 1994. [2] W.B. Scott, E.J. Crossman, Freshwater Fishes of Canada, Fish. Res. Board Can. Bull. 184, Ottawa, 1973. [3] E.T. Degens, W.G. Deuser, R.L. Haedrich, Mar. Biol. 2 (1969) 105.
195
[4] K. Simkiss, in: T.B. Bagenal (Ed.), Ageing of Fish, Unwin, London, 1974, p. 1. [5] T. Ichii, Y. Mugiya, Comp. Biochem. Physiol. 74 (1983) 259. [6] H.L. Rosenthal, M.M. Eves, O.A. Cochran, Comp. Biochem. Physiol. 32 (1970) 445. [7] N.M. Halden, J.A. Babaluk, J.L. Campbell, W.J. Teesdale, Env. Biol. Fish. 43 (1995) 333. [8] J.A. Babaluk, J.D. Reist, V.A. Sahanatien, N.M. Halden, J.L. Campbell, W.J. Teesdale, in: N.W.P. Munro, J.H.M. Willison (Eds.), Linking Protected Areas with Working Landscapes Conserving Biodiversity, Proceedings of the Third Conference on Science and Management of Protected Areas (SAMPAA), SAMPAA, Wolfville, 1998, p. 991. [9] J.D. Reist, E. Gyselman, J.A. Babaluk, J.D. Johnson, R. Wissink, Nordic J. Freshw. Res. 71 (1995) 396. [10] J.A. Babaluk, N.M. Halden, J.D. Reist, A.H. Kristofferson, J.L. Campbell, W.J. Teesdale, Arctic 50 (1997) 224. [11] N.M. Halden, J.A. Babaluk, A.H. Kristofferson, J.L. Campbell, W.J. Teesdale, J.A. Maxwell, J.D. Reist, Nucl. Instr. and Meth. B 109/110 (1996) 592. [12] J.L. Campbell, J.A. Babaluk, N.M. Halden, A.H. Kristofferson, J.A. Maxwell, S.R. Mejia, J.D. Reist, W.J. Teesdale, Nucl. Instr. and Meth. B 150 (1999) 260. [13] J.A. Babaluk, H.R. Wissink, B.G. Troke, D.A. Clark, J.D. Johnson, Arctic 54 (2001) 418. [14] L. Johnson, in: E.K. Balon (Ed.), Charrs: Salmonid Fishes of the Genus Salvelinus, Dr. W. Junk Publishers, The Hague, 1980, p. 15. [15] B.P. Kennedy, J.D. Blum, C.L. Folt, K.H. Nislow, Can. J. Fish. Aquat. Sci. 57 (2000) 2280.
Micro-PIXE analysis of strontium in Arctic char, Salvelinus alpinus, otoliths from Quttinirpaaq National Park, Nunavut, Canada J.A. Babaluk
a,*
, J.L. Campbell b, C.L. Evans a, N.M. Halden c, S.R. Mejia c, Z. Nejedly b, J.D. Reist a, W.J. Teesdale b
a
Fisheries and Oceans Canada, 501 University Crescent, Winnipeg, Manitoba, Canada R3T 2N6 Guelph-Waterloo Physics Institute, University of Guelph, Guelph, Ontario, Canada N1G 2W1 Department of Geological Sciences, University of Manitoba, Winnipeg, Manitoba, Canada R3T 2N2 b
c
Abstract Arctic char, Salvelinus alpinus, exhibit either lake resident or anadromous (sea-run) life histories. Anadromy is less prevalent at the northern and southern extremes of the distribution. Effective conservation and management of char requires knowledge of life histories exhibited by individuals and populations. Micro-PIXE line-scans were used to determine the distribution of strontium (Sr) in otoliths from which life history patterns were determined for Arctic char from 10 lakes in Quttinirpaaq National Park in the Canadian High Arctic. Although most populations were lake resident as expected, the data indicated that a component of the char population from one lake was anadromous. This represents the most northerly known char population to exhibit anadromy. Mean Sr concentrations in otoliths of char from all populations, as determined by point analysis and also from line-scan data, showed no significant differences between the methods. Mean Sr concentrations (from point analysis) showed significant differences between some of the populations. These differences combined with other analyses (e.g. morphometrics, genetics) can be used to differentiate biological populations. Thus, micro-PIXE analysis is a useful tool for assessing diversity in Arctic char and contributing to their management and conservation in the park. Ó 2002 Elsevier Science B.V. All rights reserved. PACS: 32.30.Rj; 82.80.Ej Keywords: PIXE; Proton microprobe; Fish; Otolith; Anadromy; Stock discrimination
1. Introduction A basic understanding of the biology and diversity of Arctic char, Salvelinus alpinus, popu-
*
Corresponding author. Tel.: +1-204-983-5143; fax: +1-204984-2403. E-mail address: [email protected] (J.A. Babaluk).
lations in Quttinirpaaq National Park is fundamental to Parks Canada’s long-term conservation and management plans for these fish [1]. Although Arctic char is the only freshwater fish species in the Canadian High Arctic including Quttinirpaaq National Park [2], the species exhibits great diversity at a number of levels below that of species. This includes: (a) life history type (e.g. anadromous or non-anadromous, i.e. sea-run or not),
0168-583X/02/$ - see front matter Ó 2002 Elsevier Science B.V. All rights reserved. PII: S 0 1 6 8 - 5 8 3 X ( 0 1 ) 0 1 0 4 0 - 0
J.A. Babaluk et al. / Nucl. Instr. and Meth. in Phys. Res. B 189 (2002) 190–195
191
(b) ecological type (e.g. pelagic or benthic forms), (c) trophic type (e.g. planktivore or piscivore), (d) evolutionary lineages (e.g. subspecies, biological stocks), as well as, (e) variants within many of the above types (e.g. life history variability). This diversity can be observed through a number of techniques, but is best understood and accomplished by using several complementary approaches such as: (a) morphology (e.g. body form and function), (b) genetics (e.g. delineation of groups using DNA chemistry), (c) otolith microchemistry (e.g. life history types, stocks), (d) stable isotopes and diet (e.g. trophic pattern) and (e) population dynamics (e.g. age and size structure). Otoliths (‘‘ear stones’’) are small, paired structures found in a fish’s inner ear that are used mainly to detect orientation and acceleration. They are composed mainly of a calcium carbonate (aragonite) and protein matrix; but trace elements similar to calcium (Ca), such as strontium (Sr), can be incorporated into or replace Ca in the otolith [3]. The Ca and trace elements are derived mainly from the waters that the fish inhabits [4,5]. Otoliths do not undergo resorption during the life of the fish [4]. Sea water contains, on average, 8.0 mg l1 Sr whereas freshwater contains 0.1 mg l1 Sr [6]. These differences in Sr concentrations are reflected in otolith composition. We have previously shown that they can retrospectively indicate anadromous behaviour [7] and can provide details regarding the habitats occupied early in a fish’s life [8]. A previous micro-PIXE study of Lake Hazen char otolith Sr distribution determined that both large and small forms of Lake Hazen char [9] were non-anadromous [10]. As part of an ongoing study of char ecology in the Quttinirpaaq National Park, we extended the otolith microchemistry study to: (a) determine the extent of anadromy (if any) existing within park char populations and (b) provide additional trace element, in particular Sr, information to assist in discriminating stocks or populations.
the northern end of Ellesmere Island, Nunavut (Fig. 1). The park, with an area of 37 775 km2 , is the second largest national park in Canada. There are relatively few lakes in the park and while most of these lakes provide suitable habitat for some aquatic flora and invertebrates, most are too shallow to support populations of Arctic char [1]. Our study was confined to lakes with known char populations in the area around Lake Hazen, the largest lake (540 km2 ) within the park and also the largest lake in the Canadian Arctic located completely north of the Arctic Circle. Otoliths were collected from Arctic char from 10 lakes in Quttinirpaaq National Park (Fig. 1): Lake A, Alexandra Lake, Lake B, Craig Lake, Ekblaw Lake, Lake Hazen, Heintzelman Lake, Kilbourne Lake, Lewis Lake and Murray Lake. One otolith from each of 10 char from each lake, except Lake Hazen (n ¼ 48) and Craig Lake (n ¼ 9), was prepared for micro-PIXE analysis [10]. The proton beam of the University of Guelph proton microprobe entered the otolith surface at a 45° angle. Beam energy was 3 MeV, diameter was 5–10 lm and current was approximately 5 nA. The excitation volume was approximately 30 lm in depth. The beam caused no apparent damage to the otoliths. One line-scan of Sr and other trace elements, such as zinc, K X-ray intensity for each otolith was obtained by rastering the proton beam along a transect from the core area to the dorsal edge of the otolith incorporating all yearly deposits (i.e. annuli). Three, and in some cases six, point analyses for each fish were conducted in the core area of each otolith (i.e. within the first annulus). For comparison with Sr concentrations derived from point analyses, core area Sr was also assessed by calculating the mean Sr value from the first 50 lm of the line-scan (mean of approximately 12 values for each otolith). Detection limit for Sr was 1–2 ppm. Further details on proton microprobe procedures are given in previous publications [11,12].
2. Study area, sample collection and methodology
3. Life history determination
Quttinirpaaq National Park (formerly Ellesmere Island National Park Reserve) is located at
Scanning proton microprobe transects across otoliths of known non-anadromous Arctic char in
192
J.A. Babaluk et al. / Nucl. Instr. and Meth. in Phys. Res. B 189 (2002) 190–195
Fig. 1. Map of the Lake Hazen area, Quttinirpaaq National Park showing collection locations and dates.
other areas of the Canadian Arctic and both large and small forms of Lake Hazen char showed a relatively constant and low Sr content (a ‘‘flat’’ Sr profile) from the core area to the outer edge of the otolith [10]. This suggested that these fish spent their entire life in an environment in which the Sr content was relatively constant and low (i.e. freshwater). Although Lake Hazen char have access to the sea via the Ruggles River, line-scans showed no evidence for anadromous behaviour [10; this study]. It appears that due to its length (approximately 29 km) and velocity (up to 2.25 m s1 ), the Ruggles River acts as an effective migration barrier to Lake Hazen char [13]. As expected, all char analysed from Quttinirpaaq National Park with no access (or no direct access) to the sea (Lake A, Lake B, Craig Lake, Ekblaw Lake, Kilbourne Lake and Lewis Lake) showed similar freshwater resident Sr profiles. Fig. 2 is representative of a typical Sr profile obtained from an otolith of a known non-anadromous char from one of these lakes. Although Alexandra and Murray lakes have direct outlets to the sea (Fig. 1),
Fig. 2. Typical Sr profile from a scanning proton microprobe line-scan of an otolith from a known non-anadromous Arctic char from Lake A.
all Sr line-scans from these lakes indicated only non-anadromous behaviour. An insurmountable waterfall and an extremely steep gradient prevents two-way passage of char along the outlet rivers from Murray and Alexandra lakes, respectively.
J.A. Babaluk et al. / Nucl. Instr. and Meth. in Phys. Res. B 189 (2002) 190–195
Heintzelman Lake also has direct access to the sea (Fig. 1). Nine of 10 char analysed from here exhibited typical freshwater Sr profiles (Fig. 3(a)). However, one showed a profile similar to those of known anadromous char from other areas of the Canadian Arctic (Fig. 3(b)). The pattern of Sr distribution for this 11-year-old fish had a low Sr region corresponding to the core area (within the first annulus) and the first several annuli. This region was similar to that observed for the whole otolith transect in known non-anadromous char (see Fig. 2). A marked increase in Sr corresponds to the fifth annulus, indicating that in its sixth year of life, this fish migrated to the sea; a decline in Sr within the same year (annulus) indicated that the fish returned to freshwater to over-winter. The three Sr peaks indicated that this char migrated between fresh and sea water in three consecutive years (i.e. years 6, 7 and 8). For the remaining three years of its life, it remained in freshwater. This behaviour is slightly different than most other anadromous char populations in the Canadian Arctic; most anadromous char exhibit annual migratory behaviour once they migrate to the sea for the first time [14]. The Heintzelman Lake char appears to be an example of a fish with facultative anadromous behaviour (i.e. the fish may migrate only when environmental conditions are favour-
193
able or when energetic constraints compel it to do so). More otoliths from Heintzelman Lake char will be collected and analysed to further study the anadromous behaviour regimen of this population. Based on our otolith micro-PIXE work, we suggest that the Heintzelman Lake (81°420 N, Fig. 1) char population is currently the most northern known population to exhibit anadromous behaviour. A search of pertinent literature found no reports of anadromous char at higher latitudes. However, there are several lakes further north on Ellesmere Island (within and outside the park) and also may be some in Greenland with outlets to the sea that may contain anadromous char populations. Our micro-PIXE study of char otoliths will continue as samples from these lakes are collected.
4. Stock discrimination Variation between the two methods for determining otolith core Sr (line-scan and point analyses) and between lake (population) differences is shown in Fig. 4. There were no significant differences between means for the two methods for each lake (paired t-tests). Thus, either method is suitable for determining otolith core Sr in Arctic char. Subsequent retrospective life history studies using
Fig. 3. Representative Sr profiles from scanning proton microprobe line-scans of otoliths (superimposed on optical images of the otoliths) from (a) a non-anadromous Heintzelman Lake Arctic char and (b) an anadromous Heintzelman Lake char. Annuli (age) are indicated by numbered triangles.
194
J.A. Babaluk et al. / Nucl. Instr. and Meth. in Phys. Res. B 189 (2002) 190–195
Fig. 4. Differences in mean Sr concentrations (1 standard deviation) in otolith core areas of Arctic char summarized between methods and lakes of Quttinirpaaq National Park (dots ¼ means derived from point analysis; open circles ¼ means from line-scans).
line-scans will have the added benefit of additional information for stock discrimination also being readily available. For studies that are concerned with stock discrimination only, point analysis is a more efficient method of gathering the information. Less microprobe time is required (each point analysis takes about 5 min to collect the data, whereas a typical line-scan of an Arctic char otolith requires approximately 25 min). As there were no significant differences between the two methods of determining otolith core Sr, we compared population (lake) differences by performing an analysis of variance of means derived
by point analysis. There were significant differences between Sr means for some of the lakes (Fig. 5). There were indications of at least three distinctly different groups of char in Quttinirpaaq National Park lakes: (1) Craig Lake char were significantly different from all other char except those from Lewis Lake; (2) Alexandra and Murray lakes char were not significantly different from each other but were different from all other lakes; and (3) the remaining group of lakes. Within this latter group, there were some with significant differences as well as pairs of lakes with no differences in otolith Sr concentrations. The differences in Sr concentrations might reflect differences in water Sr concentrations [4] and thus ultimately differing geology in the area. However, such variability may also result from differences in foraging activities by different forms of char within the lakes [15] and may be attributable in part to variability in char life history and small sample sizes used in our analyses. Analyses of additional fish from these locations and relating results from otolith microchemistry to local geology, and morphology and form should resolve this.
5. Conclusions Micro-PIXE analysis of Sr in Arctic char otoliths provides biologically relevant information. Mean Sr concentrations in otolith cores, as determined by point and line-scan analyses, showed no
Fig. 5. Levels of significance between pairs of lakes from analysis of variance of mean otolith core Sr concentrations as determined by point analysis (N.S.: non-significance; *: p < 0:05).
J.A. Babaluk et al. / Nucl. Instr. and Meth. in Phys. Res. B 189 (2002) 190–195
significant differences between the methods so either can be used depending on the objectives of the study. Micro-PIXE analysis of otolith Sr can retrospectively determine and assess life histories and when used with other techniques (e.g. genetics, morphology) can contribute to discrimination of stocks.
Acknowledgements This work was funded by Parks Canada and Fisheries and Oceans Canada with additional support from Natural Resources Canada (Polar Continental Shelf Project) and the Natural Sciences and Engineering Research Council of Canada.
References [1] Parks Canada, Ellesmere Island National Park Reserve Resource Description and Analysis, Department of Canadian Heritage, Winnipeg, 1994. [2] W.B. Scott, E.J. Crossman, Freshwater Fishes of Canada, Fish. Res. Board Can. Bull. 184, Ottawa, 1973. [3] E.T. Degens, W.G. Deuser, R.L. Haedrich, Mar. Biol. 2 (1969) 105.
195
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