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The deepwater faunas of oceanic islands and seamounts of the Eastern Tropical Pacific are poorly known. From 11-22 September 2009, we conducted an exploration of the deepwater areas around Isla del Coco National Park and Las Gemelas Seamount, located about 50km southwest of Isla del Coco, Costa Rica using a manned submersible to survey the seafloor habitats. The goal of the exploration was to characterize the habitats and biota, and conduct quantitative surveys of the deepwater portions of Isla del Coco National Park and Las Gemelas. We completed a total of 22 successful submersible dives, spanning more than 80hr underwater, and collected a total of 36hr of video. With respect to invertebrates, our objectives were to gather quantitative information on species composition, density, distribution and habitat associations as well as to compare the invertebrate communities between the two sites. A total of 7172 invertebrates were counted from analysis of the video collected on this project. Larger organisms were counted and placed into 27 taxonomic groups to characterize the deepwater invertebrate fauna of Las Gemelas Seamount and Isla del Coco National Park. The Shannon-Weiner Index for biodiversity (H’) was calculated to be 0.14 ± 0.02 for Isla del Coco and 0.07 ± 0.03 for Las Gemelas surveys. Although richness was fairly equal between the two sites, evenness was greater at Isla del Coco (J = 0.04 ± 0.006) when compared to Las Gemelas (J = 0.02 ± 0.01). This lower level of evenness in the community at Las Gemelas was a result of high densities of a few dominant species groups, specifically sea urchins and black corals. We also evaluated invertebrate percent cover at both Isla del Coco and Las Gemelas Seamount with respect to habitat type, slope and rugosity. Results indicated that highly rugose habitats contained the highest frequencies of all invertebrates at both sites, with the exception of glass sponges and polychaetes at Isla del Coco, which were found in greater quantities at intermediate levels of rugosity. Information obtained from these submersible surveys indicate that seamounts in the tropical eastern Pacific Ocean may be an important source of biodiversity and that more quantitative surveys are needed to characterize the fauna of the region. Citation: Starr, R.M., J. Cortés, C.L. Barnes, K. Green & O. Breedy. 2012. Characterization of deepwater invertebrates at Isla del Coco National Park and Las Gemelas Seamounts, Costa Rica. Rev. Biol. Trop. 60 (Suppl. 3): 303-319. Epub 2012 Dec 01. La fauna de aguas profundas de islas oceánicas y de montes submarinos del Pacífico Tropical Oriental son muy poco conocidas. Para caracterizar las faunas de aguas profundas del Parque Nacional Isla del Coco y el Monte Submarino Las Gemelas, Costa Rica, llevamos a cabo un estudio cuantitativo de los hábitats y su fauna. Se tomaron videos de transectos desde un sumergible entre 50 y 402m de profundidad del 11 al 22 de setiembre 2009. Se recolectó información cuantitativa de la composición de especies de invertebrados, densidad, distribución y hábitats asociados en ambas localidades y se comparó. Se contaron 7,172 invertebrados en los videos analizados, y se ubicaron en 27 categorías taxonómicas. El Índice de Shannon-Weiner (H’) fue de 0.14 ± 0.02 para la Isla del Coco y 0.07 ± 0.03 para Las Gemelas. La riqueza fue parecida en ambos sitios pero la equitabilidad fue mayor en la Isla del Coco (J = 0.04 ± 0.006) comparado con Las Gemelas (J = 0.02 ± 0.01). Este menor nivel de equitabilidad en Las gemelas de debió a la alta densidad de unos pocos grupos dominantes, específicamente erizos de mar y coral negro. También evaluamos el porcentaje de cobertura de los invertebrados con respecto a tipo de hábitat, pendiente y rugosidad del sustrato. Los resultados indican que hábitats con alta rugosidad contiene más invertebrados en ambos sitios, excepto la esponjas silíceas y los poliquetos en la Isla del Coco, que se encontraron en mayor cantidad en niveles intermedios de rugosidad. La información obtenida con este estudio indican que los montes submarinos en el Pacífico Tropical Oriental pueden ser una fuente importante de biodiversidad y que se necesitan más estudios cuantitativos para caracterizar la fauna de la región.

Predation can have substantial and long‐term effects on the population dynamics of ecologically important prey. Diverse predator assemblages, however, may produce stabilizing (i.e., portfolio) effects on prey mortality when consumption varies asynchronously among predators. We calculated spatiotemporal variation in predation on a dominant forage species to quantify synchrony and portfolio effects in a food web context and better understand diversity–stability relationships in a large marine ecosystem that has undergone considerable changes in community composition. We selected Walleye Pollock (Gadus chalcogrammus) as our case study because they support some of the largest, most valuable commercial fisheries in the world and serve as essential prey for an array of economically and culturally important species. Thus, there are sufficient data for Pollock with which to test ecological theories in an empirical setting. Spatially explicit predation indices accounted for annual variation in predator biomass, bioenergetics‐based rations, and age‐specific proportions of Pollock consumed by a suite of groundfishes in the Gulf of Alaska (1990–2015). We found that Arrowtooth Flounder (Atheresthes stomias) was, by far, the dominant Pollock predator (proportional consumption: 0.74 ± 0.14). We also found synchronous trends in consumption among predator species, indicating a lack of portfolio effects at the basin scale. This combination of a single dominant predator and synchronous consumption dynamics suggests strong top‐down control over Pollock in the Gulf of Alaska, though the degree of synchrony was highly variable at all spatial scales. Whereas synchrony generally increased in the western subregion, consumption in the central Gulf of Alaska became less synchronous through time. This suggests diminished trophic stability in one area and increased stability in another, thereby emphasizing the importance of spatiotemporal heterogeneity in maintaining food web structure and function. Finally, total Pollock consumption was highly variable (ranging from 1.87 to 7.63 Tg) and often exceeded assessment‐based estimates of productivity. We assert that using our holistic and empirically derived predation index as a modifier of assumed constant natural mortality would provide a practical method for incorporating ecological information into single‐species stock assessments.

Differences in key biological processes, such as growth and reproduction, can greatly influence localized population dynamics. Thus, it is important to evaluate intraspecific variation at several spatial scales to better understand biological limitations and develop management plans that maximize fishery sustainability. In 2011, the California Department of Fish and Wildlife (CDFW) conducted its first comprehensive stock assessment for California Halibut, Paralichthys californicus. However, limited life history data were available north of Point Conception. To improve our understanding of central California Halibut biology, 704 fish were collected during 2012 and 2013. Von Bertalanffy growth parameters were estimated at L∞ = 1041 mm and K = 0.25 for females and L∞ = 824 mm and K = 0.22 for males. Catch curve analysis indicated total mortality at 0.32 for females and 0.47 for males. Incidence of spawning females was used to estimate a seasonal spawning duration of 79 d, and temporal variation in gonadosomatic index identified peak spawning activity in July. The gravimetric method was used to estimate batch fecundity for an average-sized female (850 mm) at 6.0 x 105 eggs ± 6.7 x 104 (SE). Batch fecundity was multiplied by a spawning frequency of 25 to approximate seasonal fecundity at 1.4 x 107 eggs ± 1.3 x 106 (SE). When possible, comparisons were made with southern California Halibut using CDFW-collected data or results from the scientific literature. The information presented enhances our knowledge of California Halibut life history and provides region-specific estimates for future stock assessments.

Attributing variability in fish demographic processes to environmental conditions is helpful when assessing population status and forecasting changes in ecosystem function. Empirical orthogonal function (EOF) analysis has long been used to explore variability in physical processes, but has been only recently employed to study variability in biological processes. EOF analysis estimates dominant modes of variability (indices) and produces maps representing the spatial response for the dependent variable to each of these indices. In the eastern Bering Sea (EBS), research has linked demographic processes to the spatial extent of bottom temperatures less than or equal to 2 °C (the “cold-pool extent” or “CPE”), but has generally not compared effects among different demographic processes. We applied EOF analysis to four types of data measuring the outcome of demographic processes for EBS walleye pollock (Gadus chalcogrammus) over the period 1982–2019: numerical density (outcome of movement), morphometric condition (outcome of bioenergetics), length-at-age (outcome of growth), and prey-biomass-per-predator-mass (a proxy for stomach contents; outcome of consumption). We first designed exploratory factor analysis (EFA) models that did not include a CPE effect. We then applied confirmatory factor analysis (CFA), which differed from EFA by attributing observed patterns to a spatially varying response of demographic processes to CPE. We inferred that CPE was a proxy for demographic variability when there was a strong correlation between (1) the first or second mode of variability in the EFA and CPE or (2) the spatial map associated with the positive phase of the first or second mode of variability from the EFA model and the spatially varying response of CPE from the CFA model. Results showed that prey-biomass-per-predator-mass had the strongest correlation with CPE, numerical density and morphometric condition were also strongly correlated with CPE, and length-at-age was moderately correlated with CPE. The models also identified several anomalous years: 1999 and 2010, which were characterized by a very large CPE and high indices for variables related to demographic processes; and 2016–2019, which were characterized by a small CPE and low indices for variables related to demographic processes. We conclude that demographic processes for EBS walleye pollock show the finger-print of bottom-up environmental variation. Future research can employ CPE projections to forecast spatio-temporal changes in variables related to demographic processes, thereby informing estimates such as weight-at-age that are used in stock assessment models.

Pacific Halibut (Hippoglossus stenolepis) support culturally and economically important fisheries in the Gulf of Alaska, though recent decreases in mean size-at-age have substantially reduced fishery yields, generating concerns among stakeholders and resource managers. Among the prevailing hypotheses for reduced size-at-age is intensified competition with Arrowtooth Flounder (Atheresthes stomias), a groundfish predator that exhibited nearly five-fold increases in biomass between the 1960s and mid-2010s. To assess the potential for competition between Pacific Halibut and Arrowtooth Flounder, we evaluated their degree of spatiotemporal and dietary overlap in the Gulf of Alaska using bottom trawl survey and food habits data provided by the Alaska Fisheries Science Center (NOAA; 1990 to 2017). We restricted analyses to fish measuring 30 to 69 cm fork length and used a delta modeling approach to quantify species-specific presence-absence and catch-per-unit-effort as a function of survey year, tow location, depth, and bottom temperature. We then calculated an index of spatial overlap across a uniform grid by multiplying standardized predictions of species’ abundance. Dietary overlap was calculated across the same uniform grid using Schoener’s similarity index. Finally, we assessed the relationship between spatial and dietary overlap as a measure of resource partitioning. We found increases in spatial overlap, moving from east to west in the Gulf of Alaska (eastern: 0.13 ± 0.20; central: 0.21 ± 0.11; western: 0.31 ± 0.13 SD). Dietary overlap was low throughout the study area (0.13 ± 0.20 SD). There was no correlation between spatial and dietary overlap, suggesting an absence of resource partitioning along the niche dimensions examined. This finding provides little indication that competition with Arrowtooth Flounder was responsible for changes in Pacific Halibut alHHsize-at-age in the Gulf of Alaska; however, it does not rule out competitive interactions that may have affected resource use prior to standardized data collection or at different spatiotemporal scales.