Distribution and Life History of Spawning Capelin in Subarctic Alaska

Abstract

Capelin Mallotus villosus is a coldwater, marine forage fish that responds quickly to environmental fluctuations; however, little is known about Capelin in Alaskan waters. The objective of the current study was to better understand the distribution and life history of spawning Capelin in northern Norton Sound, Alaska. Surveys were conducted from May through July 2018 to locate and estimate the size of nearshore Capelin aggregations prior to spawning, identify the location and timing of spawning events, characterize spawning habitat, and collect actively spawning fish to examine life history characteristics (e.g., body size, age, fecundity, etc.). Most (85.9%) of the nearshore aggregations were less than 12 m 2 in surface area. Spawning Capelin were collected in Norton Sound between June 15 and June 21. At spawning locations, gravel and coarse sand accounted for over 70% of the proportional weight of sediment collected within a beach, and all sediment samples contained Capelin eggs. Spawning males were larger than spawning females in TL (mean ± SD = 148.8 ± 6.7 mm versus 137.0 ± 8.4 mm, respectively) and total weight (21.2 ± 2.9 g versus 13.7 ± 3.0 g), and both sexes were predominately age 3 (age range = 2-4 years). Absolute fecundity was 9,219 ± 4,529 eggs, and the gonadosomatic index was 1.09 ± 0.32% for males and 21.69 ± 8.21% for females. Nearshore aggregation sizes in Norton Sound were smaller than those reported for Newfoundland, but spawning behavior, timing, and water conditions were similar to observations from other Capelin spawning regions (e.g., Greenland), as were size, age, fecundity, and gonadosomatic index estimates. Although the results from the current study update baseline information on spawning Capelin in northern Norton Sound, continued research on their distribution and life history is needed to better understand ecosystem function in the North Pacific Ocean.

Endurance rivalry in capelin: insights from semen quality and regeneration

“…Capelin, despite possessing unusually small testes (Orbach et al, 2020; Ressel et al, 2020), exhibited a remarkable capacity for semen regeneration, with the majority of captive fish regenerating semen within two days (we did not assess them after one day). Individuals who did not completely replace their semen after 2 days (different individuals were sampled each day), generally continued to improve production after more time (sampling days 4 and 6).…”

“…Capelin have unusually small testes with a gonadosomatic index of around 1% (Beirão et al, 2015; Orbach et al, 2020; Ressel et al, 2020), and thus, the first scenario does not occur. We therefore predict that once spawning begins at a site, if sampled next to spawning beaches, some males will not contain any semen (used up and not yet replaced).…”

Shifts in the composition and distribution of Pacific Arctic larval fish assemblages in response to rapid ecosystem change

“…Species‐specific spawning behavior could further exacerbate northward dispersal of eggs and larvae as advection increases in warm years. For instance, populations of nearshore‐spawning yellowfin sole and capelin (Nichol & Acuna, 2001; Ressel et al, 2019) may have a greater likelihood of eggs and larvae being entrained in the northward‐flowing Alaska Coastal Current than species that spawn further offshore or along the continental slope (e.g., Pacific cod; Neidetcher et al, 2014).…”

Thermal adaptation rather than demographic history drives genetic structure inferred by copy number variants in a marine fish

“…To investigate the potential effect of CNVs on fitness‐related traits, we examined how female gonadosomatic index correlates with normalized read depth of putative CNVs using a locus‐by‐locus GWAS‐like approach. The gonadosomatic index, expressed as gonad mass as a percentage of total body mass, is widely used as a simple measure of the extent of reproductive investment and gonadal development (Brewer et al, 2008; Gunderson, 1997; Ressel et al, 2020). We used linear mixed models (LMMs) with restricted maximum likelihood optimization where the log‐transformed gonadosomatic index was introduced as the response variable and the scaled normalized read depth was included as the explanatory variable.…”

“…We first used the method developed by McKinney et al (2017) and refined by Dorant et al (2020) to detect reliable CNVs. Second, we investigated how CNV‐normalized read depth, a robust proxy of putative copy number (Dorant et al, 2020), correlates with the gonadosomatic index, a commonly used fitness proxy in fishes (Brewer et al, 2008; Ressel et al, 2020). Third, we examined the putative role of CNVs in thermal adaptation by assessing correlations between normalized read depth and water temperature in beach spawning sites.…”