Patrick Charapata

Over the last two decades, ocean warming and rapid loss of sea ice have dramatically changed the Pacific Arctic marine environment^1–3. These changes are predicted to increase harmful algal bloom prevalence and toxicity, as rising temperatures and larger open water areas are more favourable for growth of some toxic algal species⁴. It is well known that algal toxins are transferred through food webs during blooms and can have negative impacts on wildlife and human health^5–7. Yet, there are no long-term quantitative reports on algal toxin presence in Arctic food webs to evaluate increasing exposure risks. In the present study, algal toxins were quantified in bowel samples collected from 205 bowhead whales harvested for subsistence purposes over 19 years. These filter-feeding whales served as integrated food web samplers for algal toxin presence in the Beaufort Sea as it relates to changing environmental conditions over two decades. Algal toxin prevalences and concentrations were significantly correlated with ocean heat flux, open water area, wind velocity and atmospheric pressure. These results provide confirmative oceanic, atmospheric and biological evidence for increasing algal toxin concentrations in Arctic food webs due to warming ocean conditions. This approach elucidates breakthrough mechanistic connections between warming oceans and increasing algal toxin exposure risks to Arctic wildlife, which threatens food security for Native Alaskan communities that have been reliant on marine resources for subsistence for 5,000 years (ref. ⁸).

Clams are efficient vectors of potent algal neurotoxins, a suite of saxitoxin (STX) congeners collectively called paralytic shellfish toxins (PSTs), to higher trophic levels. The Alaskan Arctic is a region facing an expanding threat from PSTs due to ocean warming, yet little is known about PSTs in clams from this region. Quantifying total toxicity in bivalves requires analytical techniques, such as high-performance liquid chromatography (HPLC). Enzyme-linked immunosorbent assays (ELISAs) are an efficient but only semi-quantitative method for measuring clam toxicity. PSTs (STX eq.) were measured in split clam samples (n = 16) from the Alaskan Arctic using ELISA and HPLC methods to develop a preliminary linear model for conservatively estimating total toxicity in clams from ELISA toxin values (R²_adj = 0.95, p < 0.001). Profiles of PST congeners and total toxicity using HPLC were also assessed in additional clams (n = 36 additional, n = 52 total). Clams contained mostly potent PST congeners, and over half of the clams had PST concentrations above the seafood regulatory limit. These data will help assess the exposure risks of PSTs in Arctic marine food webs, as harmful algal bloom activity is predicted to increase as the Arctic continues to warm.

Climate change threatens fisheries health through changing ecosystem dynamics; however, the impacts on the physiology and ecology of commercial fish populations are unclear. Here, annually deposited growth increments of female yelloweye rockfish (Sebastes ruberrimus) opercula collected in the Gulf of Alaska were used to successfully reconstruct lifetime (∼1-year resolution) steroid hormone, stable isotope, spawning, and stress data. We assessed how hormone profiles, spawning and distress frequencies related to sea surface temperature (SST), chlorophyll a concentrations as well as climate indices. Further, we assessed whether incorporating indicators of foraging depth and diet, stable isotope values (ẟ¹³C and ẟ¹⁵N), would improve model interpretations. Progesterone and estradiol concentrations decreased with increasing SST, suggesting that increasing SSTs may negatively impact juvenile and subadult females’ reproductive development. Spawning frequency was positively linked to changes in the North Pacific Gyre Oscillation (NPGO) index, potentially timed with favorable conditions for larval survival. This was supported by juveniles having a lower probability of a distress event during positive NPGO years compared to negative NPGO years. While relationships among environmental data and yelloweye rockfish physiology were weak, this study provides insight into the environmental impacts on the lifetime reproduction and stress of a commercially important teleost species.

Fisheries management relies on accurate population models for estimating biomass and setting harvest goals; however, physiological data for estimating reproductive parameters in population models are difficult to acquire. Here, lifetime reproductive (progesterone and estradiol) and stress-related (cortisol) hormones were measured in annually deposited growth increments in female yelloweye rockfish ( Sebastes ruberrimus) opercula ( N = 22 females, sampled ages 1–90 years). Analyses of these profiles (∼1-year resolution) provided estimates of physiological (complete puberty) and functional age of sexual maturity (females spawn and contribute larvae to the population) and spawning frequency, with lifetime trends of reproduction and stress. The descriptive mean age of physiological sexual maturity was 11 ± 1 years (standard error (SE)), whereas functional age of maturity was 17 ± 2 years. The estimate of marginal mean spawning frequency was 45.1% ± 5.1%. Stress data (∼15% of females experienced distress events) suggested that females were potentially resilient or not exposed to chronic stressors. Although preliminary, we provide a novel method to estimate age-specific reproductive parameters for proper age-based population modeling of a human-targeted teleost.

Chemical analysis of calcified structures continues to flourish, as analytical and technological advances enable researchers to tap into trace elements and isotopes taken up in otoliths and other archival tissues at ever greater resolution. Increasingly, these tracers are applied to refine age estimation and interpretation, and to chronicle responses to environmental stressors, linking these to ecological, physiological, and life-history processes. Here, we review emerging approaches and innovative research directions in otolith chemistry, as well as in the chemistry of other archival tissues, outlining their value for fisheries and ecosystem-based management, turning the spotlight on areas where such biomarkers can support decision making. We summarise recent milestones and the challenges that lie ahead to using otoliths and archival tissues as biomarkers, grouped into seven, rapidly expanding and application-oriented research areas that apply chemical analysis in a variety of contexts, namely: (1) supporting fish age estimation; (2) evaluating environmental stress, ecophysiology and individual performance; (3) confirming seafood provenance; (4) resolving connectivity and movement pathways; (5) characterising food webs and trophic interactions; (6) reconstructing reproductive life histories; and (7) tracing stock enhancement efforts. Emerging research directions that apply hard part chemistry to combat seafood fraud, quantify past food webs, as well as to reconcile growth, movement, thermal, metabolic, stress and reproductive life-histories provide opportunities to examine how harvesting and global change impact fish health and fisheries productivity. Ultimately, improved appreciation of the many practical benefits of archival tissue chemistry to fisheries and ecosystem-based management will support their increased implementation into routine monitoring.Graphical abstract

The Pacific walrus (Odobenus rosmarus divergens) is an iconic Arctic marine mammal and an important resource to many Alaska Natives. A decrease in sea ice habitat and unknown population numbers has led to concern of the long-term future health of the walrus population. There is currently no clear understanding of how walrus physiology might be affected by a changing Arctic ecosystem. In this study, steroid hormone concentrations (progesterone, testosterone, cortisol and estradiol) were analysed in walrus bones collected during archaeological [3585–200 calendar years before present (BP)], historical [1880–2006 common era (CE)] and modern (2014–2016 CE) time periods, representing ~ 3651 years, to track changes in reproductive activity and cortisol concentrations (biomarker of stress) over time. Our results show that modern walrus samples have similar cortisol concentrations (median = 43.97 ± standard deviation 904.38 ng/g lipid) to archaeological walruses (38.94 ± 296.17 ng/g lipid, P = 0.75). Cortisol concentrations were weakly correlated with a 15-year average September Chukchi Sea ice cover (P = 0.002, 0.02, r² = 0.09, 0.04, for females and males, respectively), indicating a possible physiological resiliency to sea ice recession in the Arctic. All steroid hormones had significant negative correlations with mean walrus population estimates from 1960 to 2016 (P < 0.001). Progesterone in females and testosterone in males exhibited significant correlations with average September Chukchi Sea ice cover for years 1880–2016 (P < 0.001 for both, r² = 0.34, 0.22, respectively). Modern walruses had significantly lower (P = < 0.001) reproductive hormone concentrations compared with historic walruses during times of rapid population increase, indicative of a population possibly at carrying capacity. This is the first study to apply bone as a tool to monitor long-term changes in hormones that may be associated with changes in walrus population size and sea ice cover.