Northeast United States Continental Shelf Research Articles

Integrating fishers’ knowledge with oceanographic observations to understand changing ocean conditions in the Northeast United States

Recent warming in the Northeast United States continental shelf ecosystem has raised several concerns about the impacts on the ecosystem and commercial fisheries. In 2014, researchers from the Commercial Fisheries Research Foundation and Woods Hole Oceanographic Institution founded the Shelf Research Fleet to involve fishers in monitoring the rapidly changing ocean environment and encourage sharing of ecological knowledge. The Shelf Research Fleet is a transdisciplinary, cooperative program that trains commercial fishers to collect oceanographic information by deploying conductivity, temperature, and depth (CTD) instruments while commercially fishing. A total of 806 CTD profiles have been collected by the Shelf Research Fleet through December 2022. Participating vessels can view the conductivity and temperature water column profiles they collect in real-time. These profiles help inform their fishing practices and give insights when unexpected species appear in their gear or if their catch composition changes from previous years. The data collected by the Shelf Research Fleet are shared with and processed by researchers from numerous partnering institutions. The Shelf Research Fleet data have been used by researchers to better understand oceanographic phenomena including marine heatwaves, shelf-break exchange processes, warm core rings, and salinity maximum intrusions onto the continental shelf. The scope of the Shelf Research Fleet has grown over time to include efforts to more directly link oceanographic results with biological observations to better understand how changing ocean conditions are affecting commercially important species. This article describes the approach, successes, challenges, and future directions of the Shelf Research Fleet and aims to outline a framework for a cost-effective research program that engages fishers in the collection of oceanographic data, strengthening partnerships between fishing industry members and the scientific community.

Real-time joint ocean acoustics and circulation modeling in the 2021 New England Shelf Break Acoustics experiment (L).

During the spring of 2021, a coordinated multi-vessel effort was organized to study physical oceanography, marine geology and biology, and acoustics on the northeast United States continental shelf, as part of the New England Shelf Break Acoustics (NESBA) experiment. One scientific goal was to establish a real-time numerical model aboard the research vessel with high spatial and temporal resolution to predict the oceanography and sound propagation within the NESBA study area. The real-time forecast model performance and challenges are reported in this letter without adjustment or re-simulation after the cruise. Future research directions for post-experiment studies are also suggested.

Updated Morphological Descriptions of the Larval Stage of Urophycis (Family: Phycidae) from the Northeast United States Continental Shelf

Including early life history data in assessments can improve fisheries management by increasing our knowledge of stock structure, spawning habitat, and population trends. The identification of fish larvae to species is a necessary step in using early life history data toward this goal. Three species of hakes from the genus Urophycis are common on the northeast United States continental shelf: U. chuss or Red Hake, U. regia or Spotted Hake, and U. tenuis or White Hake. Unfortunately, identification of larval Urophycis has long been only possible at the genus level. Larvae of Urophycis (n = 277) collected in a subset of ethanol-preserved samples were identified genetically through sequencing of the cytochrome oxidase I gene and were used to update morphological descriptions with characters that separate these three species at the larval stage. Sequencing occurred in two stages: the first (n = 88) to develop a set of known-identity larvae to define species-specific traits, the second (n = 189) to test morphological identification based on the traits described in this study. We describe a combination of the location of dorsal and ventral pigment, head pigment, lower jaw pigment, and the timing of development of the pectoral fins to distinguish the larvae of these three species at sizes <6 mm. Using molecular techniques to improve morphological identifications is a powerful and efficient way to obtain the species-level data needed for assessments and management.

Comparing acoustic classification methods to estimate krill biomass in the Georges Bank region from 1999 to 2012

AbstractKrill are a critical component of northern‐latitude ecosystems, yet are poorly monitored in the Gulf of Maine and Georges Bank regions of the northeast United States continental shelf. We applied five acoustic classification methods (multifrequency single‐beam index [MFSBI], dB‐differencing, multifrequency index [MFI], and two variations of the Z‐score method) to acoustic data collected during surveys conducted annually in the Georges Bank region in order to map krill spatial distribution from 1999 to 2012. Material properties (sound speed and mass density) of krill and length data from net samples collected in the Gulf of Maine and Georges Bank regions were used in conjunction with distorted wave Born approximation (DWBA) predicted target strengths to scale acoustic data to estimates of biomass for the Georges Bank region. All methods require a priori information, ranging from training sets (i.e., empirically based classification) to validated acoustic models of target strength (i.e., theoretically based classification) for the species and acoustic frequencies of interest. Incorporating predicted backscatter from theoretical models can improve confidence in classification, especially when clean training sets are not available, but does come at the cost of a validated acoustic backscatter model. The biomass estimates from the four acoustic classification methods were comparable among each other, with the MFSBI method consistently estimating lowest biomass and the empirically based Z‐score consistently estimating highest biomass. Comparisons to net‐based estimates were inconsistent, most likely due to net inefficiency (low catchability), targeting of layers, and scaling point estimates to regions.

Effects of spring onset and summer duration on fish species distribution and biomass along the Northeast United States continental shelf

Studies documenting distributional shifts of fishes typically rely on time series of annual sampling events with fixed seasonal timing and limited temporal range. Meanwhile, as temperatures along the Northeast continental shelf have increased, the seasonal cycle also shifted towards earlier spring warming and longer summers. Seasonal migrations of fish and macroinvertebrates on the continental shelf in the Northeast US are thought to be primarily controlled by temperature and as such likely follow the temperature phenology of the shelf. This study sought to determine whether apparent changes in fish biomass and distributions are linked to spring warming phenology and/or duration of summer, the effective growing season for most species. We hypothesized that the earlier spring thermal transition would occur earlier and would cause centers of biomass to be more poleward during the spring survey. We also expected lengthening summers, primarily a function of later fall cooling, to cause centers of biomass in the fall survey to be more poleward and for biomass on the shelf to be greater within and following longer growing seasons. We did not detect a strong effect of the timing of the spring thermal transition in sea surface temperature on the distribution or abundance for most of the 43 fish stocks that we examined. However, later fall cooling and longer summers had a strong effect on both abundance and biomass of many fish stocks. These findings suggest that more focus should be placed on the length of the growing season and population-level processes that result in distributional shifts and changes in abundance.

Discovery of a spawning ground reveals diverse migration strategies in Atlantic bluefin tuna (Thunnus thynnus)

Atlantic bluefin tuna are a symbol of both the conflict between preservationist and utilitarian views of top ocean predators, and the struggle to reach international consensus on the management of migratory species. Currently, Atlantic bluefin tuna are managed as an early-maturing eastern stock, which spawns in the Mediterranean Sea, and a late-maturing western stock, which spawns in the Gulf of Mexico. However, electronic tagging studies show that many bluefin tuna, assumed to be of a mature size, do not visit either spawning ground during the spawning season. Whether these fish are spawning in an alternate location, skip-spawning, or not spawning until an older age affects how vulnerable this species is to anthropogenic stressors including exploitation. We use larval collections to demonstrate a bluefin tuna spawning ground in the Slope Sea, between the Gulf Stream and northeast United States continental shelf. We contend that western Atlantic bluefin tuna have a differential spawning migration, with larger individuals spawning in the Gulf of Mexico, and smaller individuals spawning in the Slope Sea. The current life history model, which assumes only Gulf of Mexico spawning, overestimates age at maturity for the western stock. Furthermore, individual tuna occupy both the Slope Sea and Mediterranean Sea in separate years, contrary to the prevailing view that individuals exhibit complete spawning-site fidelity. Overall, this complexity of spawning migrations questions whether there is complete independence in the dynamics of eastern and western Atlantic bluefin tuna and leads to lower estimates of the vulnerability of this species to exploitation and other anthropogenic stressors.

The role of spiny dogfish in the northeast United States continental shelf ecosystem: How it has changed over time and potential interspecific competition for resources

Abstract Ecosystem based modeling was used to determine the ecological role of spiny dogfish (Squalus acanthias), an opportunistic predator, in the northeast United States marine environment. Two time periods were modeled; one when spiny dogfish populations were depressed and one after recovery. According to our results, the ecological role of spiny dogfish has changed over time. During the depressed time period, spiny dogfish were not a keystone species and had little impact, positive or negative, on other species/groups in this ecosystem. Spiny dogfish currently have one of the highest trophic levels in this ecosystem and are akeystone species, having a high prey overlap with commercially depleted Atlantic cod (Gadus morhua). Spiny dogfish appear to have responded well to changes in this ecosystem caused by fishing and perhaps environmental change or a combination of both, while other species in the region have not. This is important, as spiny dogfish could now be potentially out competing commercially valuable and highly depleted populations of groundfish for resources. Based on our results, we suggest fisheries managers should look toward ecosystem based management measures in the future in order to actively and properly manage the ecosystem as a whole.

Changing spatial distribution of fish stocks in relation to climate and population size on the Northeast United States continental shelf

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 393:111-129 (2009) - DOI: https://doi.org/10.3354/meps08220 Changing spatial distribution of fish stocks in relation to climate and population size on the Northeast United States continental shelf Janet A. Nye1,*, Jason S. Link1, Jonathan A. Hare2, William J. Overholtz1 1National Marine Fisheries Service, Northeast Fisheries Science Center, Woods Hole Laboratory, 166 Water St., Woods Hole, Massachusetts 02543, USA 2National Marine Fisheries Service, Northeast Fisheries Science Center, Narragansett Laboratory, 28 Tarzwell Drive, Narragansett, Rhode Island 02882, USA *Email: janet.nye@noaa.gov ABSTRACT: We tested the hypothesis that recent oceanographic changes associated with climate change in the Northeast United States continental shelf ecosystem have caused a change in spatial distribution of marine fish. To do this, we analyzed temporal trends from 1968 to 2007 in the mean center of biomass, mean depth, mean temperature of occurrence, and area occupied in each of 36 fish stocks. Temporal trends in distribution were compared to time series of both local- and large-scale environmental variables, as well as estimates of survey abundance. Many stocks spanning several taxonomic groups, life-history strategies, and rates of fishing exhibited a poleward shift in their center of biomass, most with a simultaneous increase in depth, and a few with a concomitant expansion of their northern range. However, distributional changes were highly dependent on the biogeography of each species. Stocks located in the southern extent of the survey area exhibited much greater poleward shifts in center of biomass and some occupied habitats at increasingly greater depths. In contrast, minimal changes in the center of biomass were observed in stocks with distributions limited to the Gulf of Maine, but mean depth of these stocks increased while stock size decreased. Large-scale temperature increase and changes in circulation, represented by the Atlantic Multidecadal Oscillation, was the most important factor associated with shifts in the mean center of biomass. Stock size was more often correlated with the total area occupied by each species. These changes in spatial distribution of fish stocks are likely to persist such that stock structure should be re-evaluated for some species. KEY WORDS: Atlantic Multidecadal Oscillation · Climate change · Biogeography · Center of biomass · Northeast United States continental shelf · Distribution · Area–abundance relationships Full text in pdf format Supplementary material PreviousNextCite this article as: Nye JA, Link JS, Hare JA, Overholtz WJ (2009) Changing spatial distribution of fish stocks in relation to climate and population size on the Northeast United States continental shelf. Mar Ecol Prog Ser 393:111-129. https://doi.org/10.3354/meps08220Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 393. Online publication date: October 30, 2009 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2009 Inter-Research.

Changing spatial distribution of fish stocks in relation to climate and population size on the Northeast United States continental shelf

Changing spatial distribution of fish stocks in relation to climate and population size on the Northeast United States continental shelf

An approach to understanding habitat dynamics of flatfishes: Advantages of biotelemetry

The northeast United States continental shelf waters, and other coastal areas throughout the world, experience great annual temperature ranges. In response, coastal fishes, including flatfishes, make extensive migrations that are roughly delineated by the seasonal progression of tolerable isotherms. In addition to changing adult distribution, migrations affect the placement of progeny relative to highly dynamic oceanographic features with a potential for strong consequence to their recruitment success. Annual and interannual migration patterns are poorly understood for even some of the most ecologically and economically important species. In part, this is due to a lack of understanding of the variation in individual movement, whether migrants respond as a single population or as multiple contingents. The ability to monitor individual residency and movement is desirable for understanding coastal population structure. As a result of the above, our long-term goals are to determine (1) the patterns of timing, extent, and rates of migration, and (2) how these patterns are influenced by natural and anthropogenic variables. Acoustic telemetry technology is now available to track individual fish, both passively and actively, and thus effectively address these goals.

A Practice-Based Coupling of the Precautionary Principle to the Large Marine Ecosystem Fisheries Management Concept with a Policy Orientation: The Northeast United States Continental Shelf as a Case Example

This article addresses interdisciplinary sustainable aspects of fisheries as part of ocean management. Human-caused impacts and their role as modifiers of living marine resources is discussed. The research note also theorizes about contemporary global change and its prospective biological consequences, especially when coupled with human-induced factors in coastal marine waters. Also addressed is the management and ecological aspects of fish stock populations as part of a large marine ecosystem (LME) in the Northeast United States continental shelf of the Atlantic Ocean with suggestions for an interdisciplinary policy orientation paradigm to foster the sustainability of marine life in the sea.

Routes and rates of larval fish transport from the southeast to the northeast United States continental shelf

Larval fish originating south of Cape Hatteras, North Carolina, are frequently found on the continental shelf north of Cape Hatteras, even as far north as the Scotian shelf. The Gulf Stream and associated warm‐core rings are hypothesized as the physical mechanisms responsible for the northward transport of larvae. Specifically, larvae spawned along the southeast U.S. continental shelf are entrained into the Gulf Stream, transported to the northeast, regularly incorporated in warm‐core ring streamers, transported across the slope region, and released along the shelf edge north of Cape Hatteras. This proposed transport route was evaluated using hydrographic data and drifter tracks that were collected as part of other studies. Continental shelf water that originated south of Cape Hatteras was found along the edge of the Gulf Stream north of Cape Hatteras, and drifter tracks demonstrated each segment of the proposed transport route. A probability model was then developed to estimate transport times for larvae carried over the proposed transport route using a combination of sea surface temperature images, statistics of drifter transport speeds, and a larval mortality function. Modeled transport time distributions closely matched observed age distributions of larvae, further supporting the hypothesized transport route.

Reply: Does spawning stock affect recruitment of New England groundfish? Interpreting spawning stock and recruitment data in New England groundfish

Brodziak et al. 195 We offer this rejoinder to Gilbert’s (2002) discussion of our analyses of stock–recruitment data for several New England groundfish stocks (Brodziak et al. 2001). The first point that Gilbert makes—that our choice of prior probabilities affects the calculated posterior probabilities—is of course true of all Bayesian analyses. The prior odds ratio of a density-dependent stock–recruitment model being true over the range of observed data was assumed to be 2.0 in Brodziak et al. (2001) because this value was consistent with our beliefs in the relative credibility of the six stock– recruitment models examined. Based on the results of Myers and Barrowman (1996), an empirical Bayesian analysis could make an alternative argument that the prior odds ratio used by Brodziak et al. (2001) for density-independent stock–recruitment models was too ecologically optimistic. Regardless, we must point out that for 7 of the 11 stocks examined, the posterior odds ratio of a density-dependent stock–recruitment model being true over the range of observed data either increased to above 2.0 or decreased slightly to 1.78 (see table 1 of Gilbert 2002). This fact indicates that our assumed prior odds ratio was consistent with the observed data and also shows that for these stock– recruitment data, density dependence was more likely than density independence in the majority of stocks. Nonetheless, we concur with Gilbert’s implicit point that a key step in applying Bayesian analyses to natural resource management issues is selecting public policy priors. Furthermore, we submit that if Gilbert’s (1997) “recruitment-states hypothesis” is to be a credible prior belief for a specific system during a specific time period, then data and mechanisms should be presented to conclude that physical oceanographic change implies a change in fish stock dynamics (e.g., Baumann 1998). Unfortunately, Gilbert (2002) offers neither in his discussion. The second point that Gilbert (2002) makes is that the frequentist odds ratio analyses of Brodziak et al. (2001) are invalid because they do not account for the possibility that Gilbert’s recruitment-states hypothesis (or other unspecified mechanisms) could be true for the time period and system examined. This is a seemingly persuasive argument, because if the odds ratio analyses are valid, then any mediumor longer-term changes, such as a regime shift in oceanic conditions, could not have occurred under the implicit assumption that groundfish recruitment strength changes substantially from one average state to another following such a shift. Simply denying that the odds ratio analyses are valid without providing evidence of such a regime shift is a fallacy, however. If changes had occurred in the continental shelf waters off New England during the time period of our investigation, we would expect that important environmental forcing processes, such as water temperature, would have changed substantially in an obvious directional manner. Instead, water temperature anomalies for this region exhibit short-term variation on the order of a few years but do not show interdecadal time trends (Fig. 1). Furthermore, longerterm forcing variables, such as the North Atlantic Oscillation (NAO), appear to have had a limited influence on the dynamics of fish populations within the northeast United States continental shelf ecosystem in comparison to fishing activities (Link et al. 2001). Although oceanographic conditions can substantially affect recruitment of New England groundfish in any given year (see, for example, Polacheck et al. 1992), there is no conclusive evidence of any medium-term change or a sustained regime shift in the continental shelf waters off New England that would support the recruitmentstates hypothesis during the time period of our investigation. Thus, Gilbert’s rejection of our frequentist odds ratio results is not valid. We conclude by noting that our assumption that recruitment is constant over the range of observed stock sizes is not equiva-

Diets of five hake species in the northeast United States continental shelf ecosystem

We examined the diets of 5 hake species in the continental shelf ecosystem of the northeast USA: offshore hake Merluccius albidus, silver hake M. bilinearis, white hake Urophycis tenuis, red hake U. chuss, and spotted hake U. regia. We conducted a multivariate analysis of stomach contents from bottom-trawl surveys to assess the major factors that determine diet composition, to compare and contrast diets between species, and to compare the trophic role of the hakes in the northwest Atlantic to hakes in other ecosystems. These fish consume pelagic invertebrates (e.g. euphausiids and other shrimps) and pelagic fish prey, including conspecifics. The incidence of piscivory generally increases with increasing size. Regional and temporal (seasonal and yearly) variation in hake diets generally reflects differences in prey availability. Hakes are among the most abundant predators in continental shelf ecosystems worldwide. Fish prey consumption by hakes can be high and may be a primary source of mortality for economically important pelagic species. Hake predation plays an important role in the dynamics of both the US northeast continental shelf ecosystem and generally on a global scale.

Dietary guild structure of the fish community in the Northeast United States continental shelf ecosystem

Trophic guild analysis identifies groups of species that use similar resources within a community. We evaluated the trophic guild structure in an assemblage of 40 fish species in the North- east United States shelf ecosystem using a 25 yr database of food habits. We explicitly accounted for ontogenetic diet shifts by separating predator species into size classes. There were 14 significant trophic guilds. These distinguished predators based upon prey size and location in the water column (i.e., benthic to pelagic feeding). Ontogenetic diet shifts were important in guild structure, particu- larly within dominant piscivores. The mean dietary overlap both between and within guilds was notably lower than in other fish communities due to the broad spatial and temporal scale of the study, the diversity of prey types consumed, and the generalist nature of predators in this system. The guild concept is a useful framework to simplify highly connected, complex ecosystems like the Northeast US continental shelf and identify ecologically similar functional units.

Aggregations of myctophid fishes with other pelagic fauna

Direct underwater observations of myctophid fishes were conducted to 630 m in submarine canyons along the outer margin of the northeast United States continental shelf with the Johnson-Sea-Link II submersible. Data revealed that myctophids occurred in aggregations of other pelagic fauna (e.g., ctenophores, sergestids, amphipods) when densities of the former were low but the latter were high. We suggest that myctophids selectively occur with other pelagic fauna to reduce the probability of direct contact with predators and to take advantage of aggregate search abilities for common prey taxa.