Graham D. Sherwood

Slow adaptation in the face of rapid warming leads to collapse of the Gulf of Maine cod fishery.

Several studies have documented fish populations changing in response to long-term warming. Over the past decade, sea surface temperatures in the Gulf of Maine increased faster than 99% of the global ocean. The warming, which was related to a northward shift in the Gulf Stream and to changes in the Atlantic Multidecadal Oscillation and Pacific Decadal Oscillation, led to reduced recruitment and increased mortality in the region’s Atlantic cod (Gadus morhua) stock. Failure to recognize the impact of warming on cod contributed to overfishing. Recovery of this fishery depends on sound management, but the size of the stock depends on future temperature conditions. The experience in the Gulf of Maine highlights the need to incorporate environmental factors into resource management. Warming waters prevented cod recovery in the North Atlantic. Double jeopardy In the best of worlds, exploited fish stocks are monitored so that harvest quotas protect the reproductive ability of the population. Climate change is likely to complicate this process substantially. Pershing et al. found that cod stocks declined continuously during intense warming in the North Atlantic. Fisheries quotas, even though they were responsibly set and followed by fishers, decreased the reproductive rate. Thus, managing fisheries in a warming world is going to be increasingly problematic. Science, this issue p. 809

The Impact of Whaling on the Ocean Carbon Cycle: Why Bigger Was Better

Background Humans have reduced the abundance of many large marine vertebrates, including whales, large fish, and sharks, to only a small percentage of their pre-exploitation levels. Industrial fishing and whaling also tended to preferentially harvest the largest species and largest individuals within a population. We consider the consequences of removing these animals on the oceans ability to store carbon. Methodology/Principal Findings Because body size is critical to our arguments, our analysis focuses on populations of baleen whales. Using reconstructions of pre-whaling and modern abundances, we consider the impact of whaling on the amount of carbon stored in living whales and on the amount of carbon exported to the deep sea by sinking whale carcasses. Populations of large baleen whales now store 9.1×106 tons less carbon than before whaling. Some of the lost storage has been offset by increases in smaller competitors; however, due to the relative metabolic efficiency of larger organisms, a shift toward smaller animals could decrease the total community biomass by 30% or more. Because of their large size and few predators, whales and other large marine vertebrates can efficiently export carbon from the surface waters to the deep sea. We estimate that rebuilding whale populations would remove 1.6×105 tons of carbon each year through sinking whale carcasses. Conclusions/Significance Even though fish and whales are only a small portion of the oceans overall biomass, fishing and whaling have altered the oceans ability to store and sequester carbon. Although these changes are small relative to the total ocean carbon sink, rebuilding populations of fish and whales would be comparable to other carbon management schemes, including ocean iron fertilization.

Evaluation of coded microwire tag retention in juvenile American lobster, Homarus americanus

ABSTRACT The reliability of population dynamics and stock assessment models hinges on accurate life-history information. Mark-recapture studies represent a commonly used technique to investigate crustacean growth, mortality, and migrations. We evaluated tagging by coded microwire tags for the American lobster, Homarus americanus H. Milne Edwards, 1837, in a controlled study to determine tag retention and any influence on growth increment, intermolt duration, or survival. Microwire tags were injected into the propodus of the second right walking leg and two size classes (12–19.6 and 19.7–30 mm carapace length [CL]) were tested by two individual taggers. Overall tag retention was 96%. Tag retention after first ecdysis was 95% for the 12–19.6 mm CL and 92.5% for the 19.7–30 mm CL size class. There was no significant difference in tag retention between taggers, growth between tagged and untagged lobsters, or intermolt duration between tagged and untagged lobsters (P > 0.05 for all tests). Tag-induced mortality did not occur. These results support the further use of coded microwire tags to explore life-history variables for juvenile lobsters in the wild.

Response to Comments on “Slow adaptation in the face of rapid warming leads to collapse of the Gulf of Maine cod fishery”

Palmer et al. and Swain et al. suggest that our “extra mortality” time series is spurious. In response, we show that including temperature-dependent mortality improves abundance estimates and that warming waters reduce growth rates in Gulf of Maine cod. Far from being spurious, temperature effects on this stock are clear, and continuing to ignore them puts the stock in jeopardy.

Habitat Associations of Juvenile Cod in Nearshore Waters

ABSTRACT Abiotic conditions greatly influence the distribution and abundance of marine organisms during early life-history phases. For instance, factors such as habitat heterogeneity often affect the dispersive phase of marine fishes, and then diminish in importance as species approach maturity and are influenced more so by biological processes. While recently settled fish are typically found in shallow, complex habitats such as seagrass beds, the degree to which juveniles associate with specific habitats as they grow and migrate into deeper water remains less clear. To better understand fish habitat preferences during early life-history phases, a literature review was conducted on habitat use by juvenile Atlantic cod (Gadus morhua), followed by an evaluation of the relationships between habitat characteristics and bottom trawl, video and hook-and-line data in the western Gulf of Maine. The review revealed that juvenile densities, survival, and growth rates were higher in structured than in less complex habitats. Meanwhile, older juvenile cod that were sampled in the western Gulf of Maine were far more abundant on cobble and granule/pebble habitat than on mud or sand bottom. These results suggest habitat heterogeneity is tightly coupled with biological processes (e.g., predation), and its functional role extends well beyond settlement even for highly mobile species.

Distinct responses of sympatric migrant and resident Atlantic cod phenotypes to substrate and temperature at a remote Gulf of Maine seamount

Distinct responses of sympatric migrant and resident Atlantic cod phenotypes to substrate and temperature at a remote Gulf of Maine seamount Christian W. Conroy*, Jay Calvert, Graham D. Sherwood, and Jonathan H. Grabowski Marine Science Center, Department of Marine & Environmental Sciences, College of Science, Northeastern University, Nahant, MA 01908, USA Centre for Coastal and Marine Research, School of Environmental Sciences, University of Ulster, Cromore Road, Co Derry BT52 1SA, UK Gulf of Maine Research Institute, 350 Commercial St. Portland, ME 04101, USA

Patterns of larval-stage connectivity of Atlantic cod (Gadus morhua) within the Gulf of Maine in relation to current structure and a proposed fisheries closure

&NA; The decline of the Atlantic cod, Gadus morhua, stock in the Gulf of Maine to a historically low biomass has been coupled with a severe contraction in spatial range. The stock is now largely concentrated in the western Gulf of Maine. This erosion of spatial stock structure may be a factor‐inhibiting recovery of Gulf of Maine cod. However, recent efforts to rebuild anadromous forage fish in the coastal Maine region coupled with the proposed creation of a new Eastern Maine Closed Area (EMCA), sited where localized depletion of the cod stock has been especially severe, might enable reestablishment of lost spatial structure of Gulf of Maine cod. We carried out larval transport modeling to examine the potential benefit of recovered cod spawning in the EMCA through supplying larvae to suitable juvenile settlement areas in the Gulf of Maine coastal zone and in the Cashes Ledge Closed Area (CLCA) in the central Gulf of Maine. The results indicate that an appreciable fraction of the larvae spawned in the EMCA are retained, to an age of settlement capability, in the coastal Maine region. Spawning in the EMCA may thus be a contributor of juveniles to a local, eastern Gulf of Maine, cod sub‐stock. The results further indicate that spawning in the EMCA may supply a substantial subsidy of larvae to suitable juvenile habitat in the western Gulf of Maine and the CLCA. Protection of spawning stock in the EMCA may thus provide demographic benefits for the wider Gulf of Maine cod stock. Patterns of larval‐stage connectivity between various potential spawning regions (including the EMCA) and areas of suitable juvenile habitat exhibit considerable interannual variability, which is predominantly linked to variability in the large‐scale Gulf of Maine circulation. This result underscores the value of spatially explicit management as a means of fostering the recovery of the Gulf of Maine cod stock.