Salmon Ecology

Juvenile Chum and Pink Salmon Size, Growth, and Condition
Chum Salmon Early Marine Growth and Age at Entry

Juvenile Chum and Pink Salmon Ecology

Megan McPhee and Melissa Prechtl

Final Report to CIAP and BOEM:
Prechtl, M. E., Beckman, B. R., Andrews III, A. G., Beaudreau, A. H., McPhee, M. V. 2015. Growth and condition of juvenile chum and pink salmon in the northeastern Bering Sea. US Dept. of the Interior, Bureau of Ocean Energy Management, Alaska OCS Region. OCS Study BOEM 2011-AK-11-08 a/b. 59 pp. – DRAFT REPORT

Abstract:
As the Arctic continues to warm, abundances of juvenile Pacific salmon (Oncorhynchus spp.) in the northern Bering Sea are expected to increase. However, information regarding the growth and condition of juvenile salmon in these waters is limited. The first objective of this study was to describe relationships between size, growth, and condition of juvenile chum (O. keta) and pink (O. gorbuscha) salmon and environmental conditions using data collected in the northeastern Bering Sea (NEBS) from 2003-2007 and 2008-2012. Stations with greater bottom depths and cooler sea-surface temperatures were associated with greater length and lower condition (weight-length residuals) in both species, as well as greater energy density in chum salmon. Chlorophyll-a explained little variation in any measure of size or physiological condition. We used insulin-like growth factor-1 (IGF-1) concentrations as an indicator of relative growth rate for fishes sampled in 2009-2012 and that found fish exhibited higher IGF-1 concentrations in 2010-2012 than in 2009, although these differences were not clearly attributable to environmental conditions across years. Our second objective was to compare size and condition of juvenile chum and pink salmon in the NEBS between warm and cool spring thermal regimes of the southeastern Bering Sea (SEBS), based on the strong role of sea-ice retreat in the spring for production dynamics in the SEBS and prevailing northward currents, suggesting that feeding conditions in the NEBS are influenced by production in the SEBS. Chum and pink salmon were shorter and chum salmon exhibited greater energy density in years with cool springs; however, no other aspects of size and condition differed significantly between spring thermal regimes. Finally, we compared indicators of energy allocation between even and odd brood-year stocks of juvenile pink salmon to test the hypothesis that odd-year stocks allocate more energy to growing in length while even-year stocks allocate more energy to fat storage. In support of the hypothesis, even stocks of juvenile pink salmon were more energy dense, while odd stocks exhibited higher IGF-1 levels. Overall, our results support the idea that sea-ice dynamics influence energy allocation and growth of juvenile salmon in both the southern and northern Bering Sea and provide a foundation for further understanding of how environmental conditions influence juvenile salmon at the northern edge of their range.

Objectives
To assess the distribution, relative abundance, diet, energy density, and relative growth rate of juvenile pink and chum salmon utilizing the Northeastern Bering and Chukchi Seas region. In addition, variation in growth, abundance, and diet between regions will also be analyzed.

Figure 1. Southeastern Bering Sea (A) and northeastern Bering Sea (B) sea surface temperature anomalies over the past decade. These temperature regimes have a large impact on marine ecosystem funtion. In SEBS, the contrast in SST across years is more identifiable as temperature regimes are more dependant upon annual sea ice extent. In the NEBS, SST is more subdued as annual sea ice always forms in the northern region.


Figure 2. Conceptual model of interactions between growth and energy density. Considering the impact of temperature regimes on Walleye Pollock, we also hypothesize salmon condition responds in a similar fashion.


Figure 3. A) Chum and Pink Salmon followed similar trends in length over time. Differences between temperature regimes was subtle in Pink Salmon, but Chum Salmon show significant decreases in lenghth with colder temperatures. B) Energy content reflects stark differences between temperature regimes in Chum Salmon. Though, variability is too high to make a definite conclusion and could be simply related to changes in distribution in our sampling region.


Figure 4. Insulin-like Growth Factor-1 (IGF-1) levels in salmon tissue in Chum and Pink Salmon. Warm temperatures generally coinsided with higher levels of IGF-1. These results suggest conditions in these years supported growth of juvenile salmon.


Figure 5. Juvenile Pink Salmon A) energy content, B) weight/length residuals, and C) IGF-1 suggest even-year juvenile salmon are more energy dense with greater W/L residuals and lower IGF levels compared to odd-year juveniles.

The Bering Sea has alternated between warm and cool spring thermal regimes, as defined by sea surface temperature, and in recent years has remained in a “cool” state (Figure 1). Differences in spring thermal regime influence the timing of sea ice extent in the southeastern Bering Sea (SEBS) region, with warm springs facilitating early ice retreats and cool springs resulting in later ice retreat. A recent conceptual model for relating production to higher trophic levels in the SEBS proposes that during years of early sea ice retreat, phytoplankton blooms occur in warm water and support small, lipid-poor species of zooplankton. Conversely, years of late sea ice retreat results in an ice associated bloom that supports large, lipid-rich species of zooplankton.

As consequence of energy density of prey sources overwinter survival of age-0 walleye-pollock (Theragra chalcogramma) is reduced during warm years and enhanced during cool years (Hunt et al. 2011). While the northeastern Bering Sea (NEBS) has consistently supported an ice-associated bloom, it is likely that productivity in the SEBS influences trophic-level connections in the NEBS.

We extended this conceptual model to juvenile salmon and compared size and condition of juvenile chum (Oncorhynchus keta) and pink (O. gorbuscha) salmon in the NEBS between spring thermal regimes of the SEBS. We hypothesized that juvenile salmon would be longer in warm years and more energy dense in cool years. In years with cool springs, pink salmon were shorter and chum salmon exhibited greater energy density, but no other aspects of size and condition differed significantly between spring thermal regimes (Figure 2). We further examined relationships of size, growth, and condition of juvenile salmon with environmental variables within the NEBS. For both species, length increased over the time of the surveys; longer individuals were caught at greater bottom depths and in cooler sea-surface temperatures, while individuals with high length-corrected energy density were associated with cooler temperatures and shallower depths (Figure 3).

Insulin-like growth factor-1 (IGF1) levels, which provide a relative measure of growth rate, were measured from plasma derived from blood collected from juvenile pink and chum salmon. We used insulin-like growth factor-1 (IGF-1) levels as an indicator of relative growth rate for fishes sampled 2009-2012 and found fish exhibited higher IGF-1 levels between 2010-2012, than in 2009 (Figure 4). IGF-1 levels were positively correlated with temperature for juvenile chum salmon and with depth and length for juvenile pink salmon. The consistent appearance of depth (indicating distance from shore) in the best size and condition models suggested that salmon were allocating more energy to growth than fat storage over the course of our surveys. The association between cooler temperatures with greater energy density and longer lengths may reflect indirect and direct effects of temperature on salmon physiology.

Overall, recent conditions of the NEBS appear to successfully contribute to the growth and condition of the juvenile chum and pink salmon. Finally, we compared indicators of energy allocation between even and odd brood-year stocks of pink salmon and found the even brood-year stocks were more energy dense while odd brood-year stocks exhibited higher growth rates (Figure 5). These results reflect differences in energy allocation between brood-year stocks of juvenile pink salmon and suggest that the two brood-year stocks may respond differently to changing climate.

Chum Salmon Early Marine Growth and Age at Ocean Entry

Trent Sutton and Stacy Vega

Final Report to CIAP and BOEM:
Vega, S. L., Sutton, T. M., Murphy, J. M. 2016. Marine-entry timing and growth rates of juvenile Chum Salmon in Alaskan waters of the Chukchi and northern Bering seas. US Dept. of the Interior, Bureau of Ocean Energy Management, Alaska OCS Region. OCS Study BOEM 2011-AK-11-08 a/b. 47 pp.

Abstract:
Climate change in the Arctic has implications for influences on juvenile Chum Salmon Oncorhynchus keta early life-history patterns, such as altered timing of marine entry and/or early marine growth. Sagittal otoliths were used to estimate marine entry dates and daily growth rates of juvenile Chum Salmon collected during surface trawl surveys in summers 2007, 2012, and 2013 in the Chukchi and northern Bering seas. Inductively coupled plasma-mass spectrometry (ICP-MS) was used to discriminate between freshwater and marine sagittal growth on the otoliths, and daily growth increments were counted to determine marine-entry dates and growth rates to make temporal and regional comparisons of juvenile Chum Salmon characteristics. Marine-entry dates ranged from mid-June to mid-July, with all region and year combinations exhibiting similar characteristics in entry timing (i.e. larger individuals at the time of capture entered the marine environment earlier in the growing season than smaller individuals in the same region/year), as well as similar mean marine-entry dates. Juvenile Chum Salmon growth rates were on average 4.9% body weight per day in both regions in summers 2007 and 2012, and significantly higher (6.8% body weight per day) in the Chukchi Sea in 2013. These results suggest that juvenile Chum Salmon in the northern Bering and Chukchi seas currently exhibit consistent marine-entry timing and early marine growth rates, despite some differences in environmental conditions between regions and among years. This study also provides a baseline of early marine life-history characteristics of Chum Salmon for comparisons with future climate change studies.

Project Background:

Figure 1. Otoliths pulled from juvenile Chum Salmon, atop a dime for size reference.

Chum salmon, Oncorhynchus keta, are the most abundant and widely distributed Pacific salmon species and play an important role in commercial, recreational, and subsistence fisheries in Alaska. Although most Chum salmon are harvested from the Bering Sea and southeast Alaska, there is little information and few studies that have looked at their distribution as far north as the Chukchi Sea. Recent research efforts (BASIS 2007) showed higher than expected abundances of Chum salmon in the NEBS and CS regions, suggesting their potential ability to utilize available Arctic habitats in times of minimal sea ice and warmer seawater temperature.

Figure 2. Cross section of a juvenile Chum Salmon otolith. Arrows correspond to boxed portions of strontium concentrations, or the areas of strontium increase that correspond to the shift from a freshwater to a marine environment.

Additionally, a greater emphasis has been given to early marine life history research in salmonids, as little is known about salmon behavior and condition between this period of exit and re-entry into freshwater riverine and stream systems. There is currently a poor understanding of how this early marine survival effects returning Chum populations, though recent research in NEBS Chinook salmon suggests a possible link between juvenile success and returning mature salmon (Murphy et al.) This study looks to determine the age at ocean entry and early marine growth in Chum salmon, as this life history stage is likely to be very important in determining juvenile to adult survival. To address this shortfall, otolith samples (Figure 1) were taken from the 2007 BASIS cruises and 2012/2013 Arctic Eis cruises, which should provide a better understanding of early life history variation in the region with respect to a changing climate. All otolith samples were prepared (mounted and sectioned) and analyzed for marine growth (Figure 2). A subsample of otoliths will be examined using an ICP Mass Spectometer to assist in the assessment of the age at ocean entry. Sutton and Pangle’s pilot study using otolith microchemistry for Chum salmon AYK stock discrimination may also contribute to data interpretations.

The objectives for this study are as follows:

Figure 3. Length stratified average dates of ocean entry by Chum Salmon by region and year.

Objective 1: Reconstruct and compare timing of ocean entry of Chum Salmon in the Chukchi and northern Bering seas by year (2007, 2012, and 2013).

Preliminary Conclusions: Marine entry dates in the northern Bering and Chukchi Seas range from mid-June to mid-July with averages in the final week of June. Chukchi 2007 juvenile chum entered on June 26, significantly earlier than in 2012 and 2013 (Figure 3).

Figure 4. Log10 (weight, g) of juvenile Chum Salmon versus marine age (days) for each sampling year.

Objective 2: Compare growth rates between 2012/2013 Chukchi and northern Bering Sea Chum Salmon and 2007 Chukchi and northern Bering Sea Chum Salmon using daily otolith growth increments.

Preliminary Conclusions: No significant differences in weight-at-age growth relationship between any year or region combination (Figure 4).

Ultimately, this information will aid managers in making predictions on the effects of climate change on future distribution and production.

Vega et al. 2014 – AFS Meeting Poster

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