Spatial and temporal patterns in the Gulf of Alaska groundfish community in relation to the environment

Thesis (Ph.D.) University of Alaska Fairbanks, 1999The GoA supports a rich demersal fish community dominated by gadids, pleuronectids, sablefish (Anoplopoma fimbria) and rockfishes (Sebastes spp.). This study describes the structure of the juvenile and adult groundfish communities of the Gulf of Alaska (GoA) in relation to their environment and along spatial and temporal gradients. Abundance data were obtained from trawl surveys of juvenile groundfishes in the nearshore areas of Kodiak Island (1991--1996), shrimp-trawl surveys in the same areas (1976--1995), and triennial bottom trawl surveys of adult groundfishes on the GoA shelf and upper slope (1984--1996). Species richness, species diversity, total abundance, and multivariate indices of species composition for each station sampled were statistically related to depth, temperature, salinity, sediment composition, geographic location, and time of sampling to identify spatial and temporal patterns in community structure. The observed patterns were then related to local and large-scale atmospheric and oceanographic trends. Both juvenile and adult groundfish communities were primarily structured along the depth gradient. The abundance of juvenile groundfishes decreased with depth from 0 to 100m, whereas the abundance of adults increased with depth to a peak at 150--200m. Species richness and diversity of the adult community had a significant peak at 200--300m. Spatial patterns suggested higher abundances, lower species richness and diversity, and a different species composition of demersal fishes in the western GoA compared to the eastern GoA. These large-scale spatial patterns appear to be related to differences in upwelling between the eastern and western GoA. A 40% increase in total groundfish biomass on the GoA shelf and upper slope was estimated between 1984 and 1996. Significant changes in species composition occurred in the nearshore areas of Kodiak Island in the early 1980s, from a community dominated by shrimp and small forage fishes to one dominated by large piscivorous gadids and flatfishes. The change in species composition in the nearshore community appeared to be linked to an increase in advection in the Alaska Current. Increased flow around the GoA may enhance the supply of nutrients and plankton on the shelf and upper slope, resulting in an increase in overall productivity of the pelagic and demersal biota

Developing an observational design for epibenthos and fish assemblages in the Chukchi Sea

Accepted manuscript version, licensed CC BY-NC-ND 4.0. Published version available at https://doi.org/10.1016/j.dsr2.2018.11.005.In light of ongoing, and accelerating, environmental changes in the Pacific sector of the Arctic Ocean, the ability to track subsequent changes over time in various marine ecosystem components has become a major research goal. The high logistical efforts and costs associated with arctic work demand the prudent use of existing resources for the most comprehensive information gain. Here, we compare the information that can be gained for epibenthic invertebrate and for demersal fish assemblages reflecting coverage on two different spatial scales: a broader spatial coverage from the Arctic Marine Biodiversity Observing Network (AMBON, 67 stations total), and the spatial coverage from a subset of these stations (14 stations) that reflect two standard transect lines of the Distributed Biological Observatory (DBO). Multivariate cluster analysis was used to discern community similarity patterns in epibenthic invertebrate and fish communities. The 14 stations reflecting the two DBO lines captured about 57% of the epibenthic species richness that was observed through the larger-scale AMBON coverage, with a higher percentage on the more southern DBO3 than the northern DBO4 line. For demersal fishes, both DBO lines captured 88% of the richness from the larger AMBON spatial coverage. The epifaunal assemblage clustered along the south-north and the inshore-offshore axes of the overall study region. Of these, the southern DBO3 line well represented the regional (southern) epifaunal assemblage structure, while the northern DBO4 line only captured a small number of the distinct assemblage clusters. The demersal fish assemblage displayed little spatial structure with only one coastal and one offshore cluster. Again, this structure was well represented by the southern DBO3 line but less by the northern DBO4 line. We propose that extending the coverage of the DBO4 line in the northern Chukchi Sea farther inshore and offshore would result in better representation of the overall northern Chukchi epifaunal and fish assemblages. In addition, the multi-annual stability of epifaunal and, to a lesser extent also fish assemblages, suggests that these components may not need to be sampled on an annual basis and sampling every 2–3 years could still provide sufficient understanding of long-term changes. Sampling these assemblages every few years from a larger region such as covered by the AMBON project would create the larger-scale context that is important in spatial planning of long-term observing

Possible future scenarios for two major Arctic Gateways connecting Subarctic and Arctic marine systems: I. Climate and physical-chemical oceanography

We review recent trends and projected future physical and chemical changes under climate change in transition zones between Arctic and Subarctic regions with a focus on the two major inflow gateways to the Arctic, one in the Pacific (i.e. Bering Sea, Bering Strait, and the Chukchi Sea) and the other in the Atlantic (i.e. Fram Strait and the Barents Sea). Sea-ice coverage in the gateways has been disappearing during the last few decades. Projected higher air and sea temperatures in these gateways in the future will further reduce sea ice, and cause its later formation and earlier retreat. An intensification of the hydrological cycle will result in less snow, more rain, and increased river runoff. Ocean temperatures are projected to increase, leading to higher heat fluxes through the gateways. Increased upwelling at the Arctic continental shelf is expected as sea ice retreats. The pH of the water will decline as more atmospheric CO2 is absorbed. Long-term surface nutrient levels in the gateways will likely decrease due to increased stratification and reduced vertical mixing. Some effects of these environmental changes on humans in Arctic coastal communities are also presented.publishedVersio

Silver hake tracks changes in Northwest Atlantic circulation

Author Posting. © The Author(s), 2011. This is the author's version of the work. It is posted here by permission of Nature Publishing Group for personal use, not for redistribution. The definitive version was published in Nature Communications 2 (2011): 412, doi:10.1038/ncomms1420.Recent studies documenting shifts in spatial distribution of many organisms in response to a warming climate highlight the need to understand the mechanisms underlying species distribution at large spatial scales. Here we present one noteworthy example of remote oceanographic processes governing the spatial distribution of adult silver hake, Merluccius bilinearis, a commercially important fish in the Northeast US shelf region. Changes in spatial distribution of silver hake over the last 40 years are highly correlated with the position of the Gulf Stream (GS). These changes in distribution are in direct response to local changes in bottom temperature on the continental shelf that are responding to the same large scale circulation change affecting the GS path, namely changes in the Atlantic Meridional Overturning Circulation (AMOC). If AMOC weakens as is suggested by global climate models, silver hake distribution will remain in a poleward position, the extent to which could be forecast at both decadal and multidecadal scales.J.A.N. was supported by the NOAA Fisheries and the Environment program (FATE). T.M.J. and Y.O.K. were supported by the WHOI Ocean Climate Change Institute and Ocean Life Institute

Recruitment Variability in North Atlantic Cod and Match-Mismatch Dynamics

Background Fisheries exploitation, habitat destruction, and climate are important drivers of variability in recruitment success. Understanding variability in recruitment can reveal mechanisms behind widespread decline in the abundance of key species in marine and terrestrial ecosystems. For fish populations, the match-mismatch theory hypothesizes that successful recruitment is a function of the timing and duration of larval fish abundance and prey availability. However, the underlying mechanisms of match-mismatch dynamics and the factors driving spatial differences between high and low recruitment remain poorly understood. Methodology/Principal Findings We used empirical observations of larval fish abundance, a mechanistic individual-based model, and a reanalysis of ocean temperature data from 1960 to 2002 to estimate the survival of larval cod (Gadus morhua). From the model, we quantified how survival rates changed during the warmest and coldest years at four important cod spawning sites in the North Atlantic. The modeled difference in survival probability was not large for any given month between cold or warm years. However, the cumulative effect of higher growth rates and survival through the entire spawning season in warm years was substantial with 308%, 385%, 154%, and 175% increases in survival for Georges Bank, Iceland, North Sea, and Lofoten cod stocks, respectively. We also found that the importance of match-mismatch dynamics generally increased with latitude. Conclusions/Significance Our analyses indicate that a key factor for enhancing survival is the duration of the overlap between larval and prey abundance and not the actual timing of the peak abundance. During warm years, the duration of the overlap between larval fish and their prey is prolonged due to an early onset of the spring bloom. This prolonged season enhances cumulative growth and survival, leading to a greater number of large individuals with enhanced potential for survival to recruitment

Deep-Sea Fish Distribution Varies between Seamounts: Results from a Seamount Complex off New Zealand

Fish species data from a complex of seamounts off New Zealand termed the “Graveyard Seamount Complex’ were analysed to investigate whether fish species composition varied between seamounts. Five seamount features were included in the study, with summit depths ranging from 748–891 m and elevation from 189–352 m. Measures of fish species dominance, rarity, richness, diversity, and similarity were examined. A number of factors were explored to explain variation in species composition, including latitude, water temperature, summit depth, depth at base, elevation, area, slope, and fishing effort. Depth at base and slope relationships were significant with shallow seamounts having high total species richness, and seamounts with a more gradual slope had high mean species richness. Species similarity was modelled and showed that the explanatory variables were driven primarily by summit depth, as well as by the intensity of fishing effort and elevation. The study showed that fish assemblages on seamounts can vary over very small spatial scales, in the order of several km. However, patterns of species similarity and abundance were inconsistent across the seamounts examined, and these results add to a growing literature suggesting that faunal communities on seamounts may be populated from a broad regional species pool, yet show considerable variation on individual seamounts

Quantifying the Ocean, Freshwater and Human Effects on Year-to-Year Variability of One-Sea-Winter Atlantic Salmon Angled in Multiple Norwegian Rivers

Many Atlantic salmon, Salmo salar, populations are decreasing throughout the species' distributional range probably due to several factors acting in concert. A number of studies have documented the influence of freshwater and ocean conditions, climate variability and human impacts resulting from impoundment and aquaculture. However, most previous research has focused on analyzing single or only a few populations, and quantified isolated effects rather than handling multiple factors in conjunction. By using a multi-river mixed-effects model we estimated the effects of oceanic and river conditions, as well as human impacts, on year-to-year and between-river variability across 60 time series of recreational catch of one-sea-winter salmon (grilse) from Norwegian rivers over 29 years (1979–2007). Warm coastal temperatures at the time of smolt entrance into the sea and increased water discharge during upstream migration of mature fish were associated with higher rod catches of grilse. When hydropower stations were present in the course of the river systems the strength of the relationship with runoff was reduced. Catches of grilse in the river increased significantly following the reduction of the harvesting of this life-stage at sea. However, an average decreasing temporal trend was still detected and appeared to be stronger in the presence of salmon farms on the migration route of smolts in coastal/fjord areas. These results suggest that both ocean and freshwater conditions in conjunction with various human impacts contribute to shape interannual fluctuations and between-river variability of wild Atlantic salmon in Norwegian rivers. Current global change altering coastal temperature and water flow patterns might have implications for future grilse catches, moreover, positioning of aquaculture facilities as well as the implementation of hydropower schemes or other encroachments should be made with care when implementing management actions and searching for solutions to conserve this species

Increase in maturation size after the closure of a high seas gillnet fishery on hatchery-reared chum salmon Oncorhynchus keta

Gillnet fisheries are strongly size-selective and seem to produce changes in size at maturity for exploited fishes. After Word War II, large-scale gillnet fisheries targeted Pacific salmon (Oncorhynchus spp.) in the high seas area of the North Pacific and the Bering Sea, but these fisheries were closed in 1993. To assess the effects of this high seas gillnet fishery (and its closing) on size at maturity, we examined long-term trends in size at 50% probability of maturing (L50) for chum salmon (O. keta) from three populations in Hokkaido, Japan. The L50 trends were statistically different among rivers, but showed similar temporal patterns with decreases in the 1970s and early 1980s and increases after the 1985 brood year. While fishery-induced evolution seemed largely responsible for this temporal change in L50 during the fishing period, natural selection and phenotypic plasticity induced by environmental changes could contribute to the increases in L50 after the relaxation of fishing pressure