The following references are selected references that represent projects utilizing the Aquatron Laboratory’s Pool Tank.

Hutchings, J.A., and Rowe, S. 2008. Consequences of sexual selection for fisheries-induced evolution: an exploratory analysis. Evolutionary Applications 1: 129-136.

Reproductive behaviour and mating system complexity may influence fisheries-induced evolution. Mate choice and intrasexual competition might favour late-, large-maturing genotypes in contrast to the selection imposed by many fisheries. Here, we simulate changes to the mean and variance in body size of Atlantic cod (Gadus morhua) concomitant with increased fishing intensity. Comparing selection differentials (S) for length under the assumptions that size does and does not affect reproductive success, we find that the strength of selection for smaller body size associated with increased fishing pressure depends on: (i) the initial variance in body size; (ii) changes to the variance in size with increasing fishing intensity; and (iii) the influence of size on reproductive success. If the initial variability in length is sufficiently high and its coefficient of variation (CV) increases with fishing intensity, the predicted evolutionary shift towards smaller size generated by fishing is less than that expected under the assumption that reproductive success is independent of size. However, if size influences reproduction and if the CV in body size declines as fishing pressure increases, a trend that may be characteristic of many intensively exploited populations, the strength of selection for smaller size is predicted to be comparatively rapid. We conclude that fisheries-induced evolution can be influenced by changes to the mean and variance of traits under sexual selection, and that the benefits of maintaining broad phenotypic variability in traits such as body size may be greater than previously thought.

Rowe, S., and Hutchings, J.A. 2008. A link between sound producing musculature and mating success in Atlantic cod. Journal of Fish Biology 72: 500-511.

Individual variability in the mating success of male Atlantic cod Gadus morhua was quantified within an aggregation (n ¼ 59) breeding undisturbed in a large (684 m 3) mesocosm tank. Observational and morphometric data were examined to assess the degree to which this mating variation could be explained by aspects of morphology, condition and spawning behaviour. The number of ventral mounts initiated (i.e. mating success) was highly variable; most mounts were initiated by a very small percentage of available males. The significant correlate of male mating success was mass of the sound producing musculature, i.e. drumming muscles. Neither body size, condition, pelvic and median fin morphology nor aggression influenced the number of ventral mounts initiated by a male. The present study suggests a possible link between sound production and mating success in Atlantic cod.


Rowe, S., Hutchings, J.A., Skjæraasen, J.E., and Bezanson, L. 2008. Morphological and behavioural correlates of reproductive success in Atlantic cod Gadus morhua. Marine Ecology Progress Series 354: 257-265

We tested the hypothesis that reproductive success is randomly distributed within spawning aggregations of Atlantic cod Gadus morhua, a broadcast-spawning marine fish for which no parental care is provided. Based on microsatellite DNA-parentage assignment of 8913 offspring from 4 large (n = 52 to 93) experimental spawning aggregations, we quantified individual variation in male reproductive success and evaluated the degree to which this variation could be explained by aspects of morphology, condition, and spawning behaviour. Reproductive success was highly skewed, with more than 80% of the offspring within each group sired by 2 to 7 individuals. Body size and agonistic interactions initiated were positively associated with male reproductive success within each group. The lengths of fins prominent during courtship and mating were also correlated with reproductive success within one of the spawning groups for which data were available. Our observations are consistent with the hypotheses that some form of intrasexual competition or mate choice is a constituent of the mating system of this species and that the ratio of effective to census population size in broadcast-spawning marine fishes is very small.

Hutchings, J.A., Swain, D.P., Rowe, S., Eddington, J.D., Puvanendran, V., and Brown, J.A. 2007. Genetic variation in life-history reaction norms in a marine fish. Proceedings of the Royal Society B 274: 1693-1699

Neither the scale of adaptive variation nor the genetic basis for differential population responses to the environment is known for broadcast-spawning marine fishes. Using a common-garden experimental protocol, we document how larval growth, survival and their norms of reaction differ genetically among four populations of Atlantic cod (Gadus morhua). These traits, and their plastic responses to food and temperature, differed across spatial scales at which microsatellite DNA failed to detect population structure. Divergent survival reaction norms indicate that warm-water populations are more sensitive to changes in food, whereas cold-water populations are more sensitive to changes in temperature. Our results suggest that neither the direction nor the magnitude of demographic responses to environmental change need be the same among populations. Adaptive phenotypic plasticity, previously undocumented in marine fishes, can significantly influence the probability of recovery and persistence of collapsed populations by affecting their ability to respond to natural and anthropogenic environmental change.

Hardie, D.C., Gillett, R.M., and Hutchings, J.A. 2006. The effects of isolation and colonization on the genetic structure of marine-relict populations of Atlantic cod (Gadus morhua) in the Canadian Arctic. Canadian Journal of Fisheries and Aquatic Sciences 63: 1830-1839

The genetic consequences of extended periods at low population size are fundamental to the conservation of depleted species such as the Atlantic cod (Gadus morhua). We compared microsatellite genetic variability among cod populations in Canadian Arctic lakes with that of Gilbert Bay resident and inshore cod from eastern Canada. The Arctic populations had the lowest genetic diversity and were the most strongly genetically structured and distinct. By contrast, eastern Canadian samples expressed high allelic diversity and were not significantly genetically structured or distinct relative to each other, whereas Gilbert Bay resident cod were intermediate to the Arctic and eastern Canadian groups. Our results are consistent with the hypothesis that the Arctic populations were colonized between 8000 and 5000 years ago and have experienced little or no gene flow since that time. Despite isolation at the extreme of the species’ range, the Arctic populations have retained relatively high heterozygosities and high genetic effective population sizes relative to census sizes (Ne –Nc ratios). Potential explanations for this include the absence of fishing pressure, allowing for the persistence of large, highly fecund individuals, as well as biotic (e.g., absence of planktivores) and abiotic (e.g., low environmental stochasticity) factors in the Arctic lakes that minimize individual variance in reproductive success.

Marcil, J., Swain, D.P., and Hutchings, J.A. 2006. Genetic and environmental components of phenotypic variation in body shape among populations of Atlantic cod (Gadus morhua L.). Biological Journal of the Linnean Society 88:351-36

A common-garden experiment was conducted on larvae to test for genetic differences in body shape among populations of Atlantic cod ( Gadus morhua ). Offspring from four north-west Atlantic regions were reared from hatching to post metamorphosis at two temperatures (7 ± 1 ° C and 11 ± 1° C) and two food levels (1500 and 4500 prey L − 1 ). Body shape differed between populations and treatments. Population differences were greatest between south-west Scotian Shelf cod and those further north; the former were characterized by a deeper body, larger head, and longer caudal peduncle than cod from the other populations. Significant differences were also observed between two putative populations on the south-west Scotian Shelf, suggesting genetic divergence between spawning aggregations at small spatial scales ( < 100 km). Temperature and food supply also influenced body shape, with the effect of the former being more pronounced. Individuals reared at the higher temperature or food level had a deeper body and a larger head than those reared at the lower temperature or food supply. Phenotypic responses to changes in the rearing environment also differed among populations, indicating genetic differences in phenotypic plasticity. Differences between populations in morphology and in phenotypic plasticity suggest genetic divergence at both large ( > 1000 km) and small ( < 100 km) spatial scales. The genetic differences at large spatial scales counteracted the expected effects of temperature differences in the wild, suggesting counter gradient variation in morphology among these populations.


Marcil, J., Swain, D.P., and Hutchings, J.A. 2006. Countergradient variation in body shape between two populations of Atlantic cod (Gadus morhua). Proceedings of the Royal Society B 273: 217-223.

Variation in morphological traits is generally thought to be cogradient, with environmental effects on phenotypic expression reinforcing genetic differences between populations. We compared body shape between two populations of Atlantic cod (Gadus morhua). Striking shape differences occurred between juveniles from the two populations when reared in a common laboratory environment. However, no difference in body shape occurred between wild-reared juveniles from the two populations, suggesting that the genetic differences between populations were obscured by opposing effects of the environmental differences experienced in the wild. We suggest that much of the genetic diversity in body shape of fishes may be cryptic, with stabilizing selection for the same optimal phenotype resulting in genetic divergence between populations subject to contrasting environmental influences.


Rowe, S., and Hutchings, J.A. 2006. Sound production by Atlantic cod during spawning. Transactions of the American Fisheries Society 135: 529-538

Using captive groups of Atlantic cod Gadus morhua from two Northwest Atlantic populations (western Scotian Shelf and southern Gulf of St. Lawrence), we quantified the temporal patterns and behavioural contexts of sound production during the spawning season. We found that sound production occurs most frequently during the peak of the spawning period, particularly after the onset of darkness. The rate of sound production by males in the western Scotian Shelf group was 8.4 times greater on average than that of the southern Gulf of St. Lawrence group, and this corresponded to differences in the mass of the sound-producing musculature. Based on behavioural observations during daylight hours, we found that sounds were associated with both courtship behaviour and agonistic displays. Although sounds were produced on only 14.5% of the occasions in which a male and female swam together in a ‘‘ventral mount,’’ limited data suggest that ventral mounts accompanied by sound were more likely to lead to spawning. While almost all sounds produced by Atlantic cod in our study matched the short ‘‘grunt’’ type previously documented for this species, we report evidence for another sound, described as a ‘‘hum,’’ which occurs during the ventral mount immediately before gamete release. We hypothesize that sound production is related to competition among males for access to females and may help synchronize gamete release, underscoring the potential importance of sound production to Atlantic cod spawning behaviour.

Rowe, S., Hutchings, J.A., Bekkevold, D., and Rakitin, A. 2004. Depensation, probability of fertilization, and the mating system of Atlantic cod. ICES Journal of Marine Science 61: 1144-1150

Atlantic cod (Gadus morhua L.) have been severely overexploited and are currently at historic population lows, having declined 90% in the North Sea and 99% off northeast Newfoundland in recent decades. Slow rates of recovery and continuing declines may be attributable to depensation, defined as a reduction in per capita growth rate concomitant with reduced population size. Several potential causes of depensation relate to low mating success and consequent reduced production of offspring. We explore the empirical basis of one of these in Atlantic cod using egg fertilization and male abundance data obtained from 21 experimental populations generated by three independent research programmes. We find support for the hypotheses that (a) fertilization rate declines with abundance and (b) variance in fertilization rate increases as population size declines. The former identifies one potential mechanism underlying depensation in Atlantic cod. The latter has negative genetic consequences for effective population size (Ne), resulting in a decline in the ratio of Ne to census population size (Ne/Nc) with declining abundance. Our results may have general implications for the conservation biology of broadcast-spawning marine fish, particularly those with mating systems similar to that of Atlantic cod.


R. K. O’Dor, R. D. Durward and D B. Steadman, Laboratory Studies on the Life Cycle and Vertical Migration of the Squid, Illex illecebrosus. International Council for the Exploration of the Sea C. M. 1977/K:9 Shellfish and Benthos Committee.

Eighty-five squid were observed for periods of up to 82 days in the in the 15 m diameter pool tank in the Aquatron Laboratory. Animals remained in excellent condition and grew at rates comparable to the wild population, eating 20% of body weight in frozen fish per day. Captive females matured in as little as 80 days after an increase in photoperiod on entry to the tank. Rapid maturation and small egg size fit with the one year life cycle proposed from limited field data. Squid kept in the 10 m deep tower tank showed distinct nocturnal ascent, a behaviour also tentatively suggested by field data. The characteristics of the facility which allow for long term maintenance of squid are described and other experimental procedures feasible in the facility outlined. Interested researchers are invited to make use of the Aquatron Laboratory for studies on captive populations of cephalopods.


O'Dor, R., Foy, E., Helm, PL., Balch, N. 1986. The locomotion and energetics of hatchling squid, Illex illecebrosus. American Malacological Bulletin. 4: 55-6035.

Although never seen in nature, gelatinous egg masses up to 1 m in diameter containing 10,000 to 100,000 eggs have been produced in captivity by female llex illecebrosus swimming in mid-water in the 15 m diameter Aquatron pool. When incubated at temperatures between 13 and 26 degree C these masses produced viable hatchlings whose behaviours were observed and recorded. The hatchlings sink at 5 mm s super (-1), swim vertically at speeds up to 26 mm s super (-1), hover and avoid both the surface and the bottom. Metabolic rates estimated from rates of yolk utilization and calculated values for swimming costs were used to predict "critical periods" or survival times for unfed hatchlings in various temperature and activity regimes. These are discussed in relation to the hypothesized role of the Gulf Stream in distribution of the hatchlings of this commercially important but still poorly understood squid species.


J. Marcus, W. Don Bowen, J. D. Eddington.1997. Effects of Meal Size on Otolith Recovery from Fecal Samples of Gray And Harbour Seal Pups. Marine Mammal Science. 14:4:789 – 802

Recovered otoliths from pinniped feces provide valuable information on diet composition and prey size. We studied the effect of meal size on otolith recovery from the feces of one harbor and eight gray seal pups. Each of 11 experiments comprised a half-ration meal, a period of fecal collection, a 1.5- or double-ration meal again followed by a period of fecal collection. A significantly lower percentage of Atlantic herring otoliths were recovered from half-ration meals (25% 5 12.5% in the harbor seal, 8.6% 2 6.9% in eight gray seals) than from 1.5- or double-ration meals (62.5% 5 3.1 % in the harbor seal, 32.8% -C 23.5% in gray seals). Meal size also significantly affected the percentage of Atlantic cod otoliths recovered from gray seal feces (65.0% 5 26.3% from half ration, 98.3% 5 2.9% from 1.5 ration). For both size meals, recovered cod otoliths were more significantly eroded than herring otoliths. The development of correction factors to account for the effects of digestion will need to consider the distribution of meal sizes of free-ranging pinnipeds.

R. G. Brown, W. D. Bowen, J. D. Eddington, W. C. Kimmins, M. Mezei, J. L. Parsons and B. Pohajdak. 1997. Evidence for a long-lasting single administration contraceptive vaccine in wild grey seals. Journal of Reproductive Immunology.35:1:43-51.

A single-administration birth control vaccine based on liposome delivery of porcine zona pellucida antigens reduced pup production in grey seals (Halichoerus grypus) by about 90%. Anti-porcine zona pellucida titers of individual seals with two or more recaptures were variable but without a diminishing trend during the 5 year post-immunization period. Seals that produced at least one or more pups during the 2–5 year post-immunization period when the vaccine is fully effective had an average anti-porcine zona pellucida titer of 5% of the reference serum. In contrast, the subset of seals that did not reproduce but were recaptured during the breeding season had an average titer of 31% of the reference serum. As measured by antibody titers and pup production, there were no differences in efficacy of the vaccine in 14-, 20- and 21-year-old female grey seals.

R. G. Brown, W. D. Bowen, J. D. Eddington, W. C. Kimmins, M. Mezei, J. L. Parsons and B. Pohajdak. 1997. Temporal trends in antibody production in captive grey, harp and hooded seals to a single administration immunocontraceptive vaccine. Journal of Reproductive Immunology .35:1:53-64.

The temporal production of antibody to a single-administration immunocontraceptive vaccine, known to be immunocontraceptive in free-ranging female grey seals (Halichoerus grypus), was studied in captive grey seals, harp seals (Phoca groenlandica) and hooded seals (Cystophora cristata). The vaccine is based on liposome delivery of porcine zona pellucida antigens. When measured by antigen capture, the response of hooded and harp seals to the vaccine were similar to the response of grey seals. Determination of antibody production by ELISA with protein A, ELISA with rabbit anti-seal immunoglobulin sera and SDS-PAGE after affinity chromatography confirmed the similarity in response to the vaccine by grey and harp seals, but suggested lower titers in hooded seals. The vaccine produced titers in captive, juvenile grey and harp seals known to be immunocontraceptive in wild, adult grey seals.

Danielle K. Greave, Michael O. Hammill, Jim D. Eddington, Darcy Pettipas, Jason F. Schreer. 2003. Growth Rate and Shedding of Vibrissae in the Gray Seal, Halichoerus Grypus: A Cautionary Note For Stable Isotope Diet Analysis. Marine Mammal Science. 20:2:296-304.

Stable isotopes have become powerful tools for gathering information on food webs in marine ecosystems. The method is based on the concept that the ratio of Nitrogen-14 to 15N (or Carbon-12 to 13C) in the tissues of animals is directly related to the ratio found in their diet. Vibrissae provide a time series of stable isotope data as tissue is laid down sequentially over time. Here we examine the growth rate of 283 mystacial (muzzle) vibrissae of four gray seals, Halichoeruas grypus, over a five-month period to investigate their applicability for stable isotope diet analysis. The individual vibrissae did not grow at a constant rate during the study, Fifty-nine actively growing vibrissae were modeled to quantify the growth pattern using a three-parameter von Bertalanffy curve, with the parameters estimated using non-linear mixed-effects models. This model incorporated the inherent serial correlation of these data. The growth rate was 0.024 cm/d (95% CI = 0.019–0.030), the asymptotic length differed significantly by location (F3, 56=9.64, P < 0.001), but no significant trend was found with muzzle location (F3, 56= 0.15, P= 0.93). The Δlength/Δtime between each measurement was calculated and most of these data fell at or near zero growth (median = 0.04 cm/d, range = 0–0.78). Individual vibrissae were shed asynchronously and without any seasonal growth trend. This has serious implications for researchers attempting to extrapolate diet data from vibrissae. Because the growth is neither continuous nor synchronous, it will be a challenge to accurately identify the dates when the isotopes were incorporated into the tissue.

Sara J. Iverson, Chris Field, W. Don Bowen, Wade Blanchard (2004) Quantitative Fatty Acid Signature Analysis: A NEW METHOD OF ESTIMATING PREDATOR DIETS. Ecological Monographs: Vol. 74, No. 2, pp. 211-235.

Accurate estimates of the diets of predators are required in many areas of ecology, but for many species current methods are imprecise, limited to the last meal, and often biased. The diversity of fatty acids and their patterns in organisms, coupled with the narrow limitations on their biosynthesis, properties of digestion in monogastric animals, and the prevalence of large storage reservoirs of lipid in many predators, led us to propose the use of quantitative fatty acid signature analysis (QFASA) to study predator diets. We present a statistical model that provides quantitative estimates of the proportions of prey species in the diets of individual predators using fatty acid signatures. We conducted simulation studies using a database of 28 prey species (n = 954 individuals) from the Scotian Shelf off eastern Canada to investigate properties of the model and to evaluate the reliability with which prey could be distinguished in the model. We then conducted experiments on grey seals (Halichoerus grypus, n = 25) and harp seals (Phoca groenlandica, n = 5) to assess quantitative characteristics of fatty acid deposition and to develop calibration coefficients for individual fatty acids to account for predator lipid metabolism. We then tested the model and calibration coefficients by estimating the diets of experimentally fed captive grey seals (n = 6, switched from herring to a mackerel/capelin diet) and mink kits (Mustela vison, n = 46, switched from milk to one of three oil-supplemented diets). The diets of all experimentally fed animals were generally well estimated using QFASA and were consistent with qualitative and quantitative expectations, provided that appropriate calibration coefficients were used. In a final case, we compared video data of foraging by individual free- ranging harbor seals (Phoca vitulina, n = 23) fitted with Crittercams and QFASA estimates of the diet of those same seals using a complex ecosystem-wide prey database. Among the 28 prey species in the database, QFASA estimated sandlance to be the dominant prey species in the diet of all seals (averaging 62% of diet), followed primarily by flounders, but also capelin and minor amounts of other species, although there was also considerable individual variability among seals. These estimates were consistent with video data showing sandlance to be the predominant prey, followed by flatfish. We conclude that QFASA provides estimates of diets for individuals at time scales that are relevant to the ecological processes affecting survival, and can be used to study diet variability within individuals over time, which will provide important opportunities rarely possible with other indirect methods. We propose that the QFASA model we have set forth will be applicable to a wide range of predators and ecosystems.

Margaret H. Cooper, Sara J. Iverson, Horacio Heras. 2004. Dynamics of blood chylomicron fatty acids in a marine carnivore:implications for lipid metabolism and quantitative estimation of predator diets. J Comp Physiol B (2005) 175: 133–145.

Blubber fatty acid(s) (FA) signatures can provide accurate estimates of predator diets using quantitative FA signature analysis, provided that aspects of predator FA metabolism are taken into account. Because the intestinal absorption of dietary FA and their incorporation into chylomicrons (the primary transport lipoproteins for dietary FA in the blood) may influence the relationship between FA composition in the diet and adipose tissue, we investigated the metabolism of individual FA at these early stages of assimilation. We also investigated the capacity of chylomicron signatures to provide quantitative estimates of prey composition of an experimental meal. Six captive juvenile grey seals (Halichoerus grypus) were fed either 2.3 kg (n=3) or 4.6 kg (n=3) of Atlantic herring (Clupea harengus). Although chylomicron FA signatures resembled diet signatures at all samplings, absolute differences were smallest at 3-h post-feeding, when chylomicrons were likely largest and had the greatest ratio of triacylglycerol to phospholipid FA. Specific FA that differed significantly between diet and chylomicron signatures reflected either input from endogenous sources or loss through peroxisomal b-oxidation.When these aspects of metabolism were accounted for, the quantitative predictions of diet composition generated using chylomicron signatures were extremely accurate, even when tested against 28 other prey items.
B. D. Johnson and P. J. Wangersky. 1985. Seawater Filtration: Particle Flow and Impaction Considerations. Limnology and Oceanography, Vol. 30, No. 5 (Sep., 1985), pp. 966-971.