More Like this

1. Juvenile Albacore tuna ( Thunnus alalunga ) foraging ecology varies with environmental conditions in the California Current Large Marine Ecosystem

   https://doi.org/10.1111/fog.12638  

   Nickels, Catherine F. ; Portner, Elan J. ; Snodgrass, Owyn ; Muhling, Barbara ; Dewar, Heidi ( September 2023 , Fisheries Oceanography)

   Juvenile North Pacific Albacore tuna (Thunnus alalunga) support commercial and recreational fisheries in the California Current Large Marine Ecosystem (CCLME), where they forage during summer and fall. The distributions of the commercial and recreational fisheries and estimates of forage availability have varied substantially over the past century. Time‐series quantifying Albacore diet can help link forage composition to variability in Albacore abundance and distribution and, consequently, their availability to fishers. Previous diet studies in the CCLME are of relatively short duration, and long‐term variability in Albacore diet remains poorly understood. We describe the diets of juvenile Albacore from three regions in the CCLME from 2007 to 2019 and use classification and regression tree analysis to explore environmental drivers of variability. Important prey include Northern Anchovy (Engraulis mordax), rockfishes (Sebastesspp.), Boreal Clubhook Squid (Onychoteuthis borealijaponica), euphausiids (Order: Euphausiidae), and amphipods (Order: Amphipoda), each contributing >5% mean proportional abundance. Most prey items were short lived species or young‐of‐the‐year smaller than 10 cm. Diet variability was related to environmental conditions over the first 6 months of the year (PDO, sea surface temperature, and NPGO) and conditions concurrent with Albacore capture (region and surface nitrate flux). We describe foraging flexibility over regional and annual scales associated with these environmental influences. Continuous, long‐term studies offer the opportunity to identify flexibility in Albacore foraging behavior and begin to make a predictive link between environmental conditions early in the year and Albacore foraging during summer and fall.

    

   more » « less
2. Trophic ecology of Humboldt squid, Dosidicus gigas , in conjunction with body size and climatic variability in the Gulf of California, Mexico

   https://doi.org/10.1002/lno.11343  

   Portner, Elan J. ; Markaida, Unai ; Robinson, Carlos J. ; Gilly, William F. ( October 2019 , Limnology and Oceanography)

   Over the past two decades, the Gulf of California (GOC) has experienced three strong El Niño events (1997–1998, 2009–2010, and 2015–2016), each of which was followed by a drastic reduction in mantle length of mature Humboldt squid,Dosidicus gigas(from >60 cm to <20 cm). However, it is unclear how the oceanographic changes associated with strong El Niño events affected the midwater organisms on whichD. gigasfeed, limiting our ability to assess the relative importance of temperature and food availability in the phenotypic response ofD. gigasto environmental variability. We quantified the diet ofD. gigasin the GOC before, during, and following the past three El Niño events and found that although its diet varied little across a large range of body sizes (8–85 cm), significant and predictable diet variability was observed with respect to sea surface temperature and chlorophyll‐a concentration. Consumption of large numbers of relatively small, high calorie prey in both relatively cool (anchovies) and relatively warm, productive conditions (myctophids) is likely necessary to support growth to large body sizes before maturation. When warm, unproductive conditions prevailed in the GOC, only small squid were present and had diets dominated by euphausiids and pteropods, prey with relatively low caloric value. Using a time series of diet data, this work provides unique insights into the response of a midwater forage community to oceanographic variability and the effects of environmental variability on the trophic ecology of an oceanic predator.

    

   more » « less
3. Gelatinous cephalopods as important prey for a deep-sea fish predator

   https://doi.org/10.1007/s00227-022-04116-w  

   Chen, Rachel S. ; Portner, Elan J. ; Choy, C. Anela ( November 2022 , Marine Biology)

   We quantified cephalopods consumed by longnose lancetfish (Alepisaurus ferox,n = 1267 stomachs containing cephalopod remains) from 2009 to 2018 in the central North Pacific Ocean (between 0–35° N and 135–175° W). When cephalopods identified from beak remains in the stomach contents were included in diet analyses, clear increases in the abundance of gelatinous taxa and the inferred foraging depths of lancetfish were evident. Ontogeny in cephalopod consumption was evident for lancetfish, corroborating past diet studies. Small lancetfish (fork length < 97 cm) fed on smaller, muscular cephalopods from shallow habitats (0–500 m, e.g., Ommastrephidae, Onychoteuthidae), while large lancetfish (fork length ≥ 97 cm) consumed larger, gelatinous cephalopods from deeper waters (depths greater than 500 m, e.g., Amphitretidae, Cranchiidae). Cephalopod beaks were more abundant in the diets of large lancetfish, representing 37.8% of identified cephalopods, numerically. Although beaks likely remain in stomachs longer than soft tissues, they did not simply accumulate with increasing predator size. Cephalopods identified from beaks were also significantly larger than those identified from soft tissues. Despite having low average energy densities, large gelatinous cephalopods are important prey for lancetfish in deep habitats, with energetic values that are comparable to smaller, more muscular cephalopods (95.3 ± 125.8 kJ and 120.2 ± 169.4 kJ, respectively). Holistic consideration of cephalopod beaks in diet analyses will help to elucidate predator foraging behaviors and the trophic and ecological roles of gelatinous cephalopods in deep pelagic food webs.

    

   more » « less
4. Examining the ecological role of jellyfish in the Eastern Bering Sea

   https://doi.org/10.1093/icesjms/fsz244  

   Ruzicka, James ; Brodeur, Richard D. ; Cieciel, Kristin ; Decker, Mary Beth ; Ji, ed., Rubao ( December 2019 , ICES Journal of Marine Science)

   Within the Eastern Bering Sea, the jellyfish Chrysaora melanaster has fluctuated widely over recent decades. We examined the role of C. melanaster as an ecosystem-structuring agent via application of ecosystem models representing inner-, mid-, and outer-shelf regions of comparable areal coverage. Chrysaora melanaster utilize 1% of total mid-shelf consumer production, or 1/4th the energy required by forage fish (capelin Mallotus villosus, Pacific herring Clupea pallasii, age-0 Pacific cod Gadus macrocephalus, age-0 walleye pollock Gadus chalcogrammus). Model simulations show the impacts of C. melanaster are broadly distributed across consumer groups with increasingly negative impacts with higher jellyfish biomass. Age-0 pollock represent the greater part of the forage fish biomass, and observed pollock biomass during low jellyfish years (2004–2007) was significantly greater than during high jellyfish years (2009–2014). However, sensitivity among consumer groups to observed jellyfish variability is small, within 5% of baseline (2004–2015) conditions. Estimates using similar models for the Coastal Gulf of Alaska (CGoA) and Northern California Current (NCC) suggest large differences in the role of scyphozoans among northern Pacific shelf ecosystems. Only 0.1% of total summer consumer production is required to support CGoA Chrysaora, while the coastal NCC population uses 19%.

    

   more » « less
5. Marine heatwaves alter the nursery function of coastal habitats for juvenile Gulf of Alaska Pacific cod

   https://doi.org/10.1038/s41598-024-63897-w  

   Thalmann, Hillary_L ; Laurel, Benjamin_J ; Almeida, L_Zoe ; Osborne, Kaitlyn_E ; Marshall, Kaylee ; Miller, Jessica_A ( June 2024 , Scientific Reports)

   Marine Heatwaves (MHWs) can directly influence survival of marine fishes, particularly for early life stages, including age-0 juveniles during their residence in coastal nursery habitats. However, the ability of nurseries to support high fish densities, optimize foraging and growth, and protect against predators may be altered during MHWs. Gulf of Alaska Pacific cod (Gadus macrocephalus) larval, juvenile, and adult abundances declined dramatically following MHW events in 2014–2016 and 2019. To evaluate coastal nursery function during MHWs, we compared diet composition, recent growth, size, condition, and abundance of age-0 juveniles throughout their first summer before, during, and between MHWs. Diet shifted to larger prey during MHWs, particularly mysids, but diet did not appear to influence growth. We observed faster growth rates during MHWs, yet even when accounting for growth, we could not explain the higher body sizes observed in August during MHWs. Together with lower abundance and the near absence of small fish in the nursery by August during MHWs, these patterns highlight potential for size-selection and a reduced ability of nursery habitats to buffer against environmental variability during MHWs, with only a small number of large “super survivors” persisting through the summer.

    

   more » « less