Marine fisheries refugia, unaltered areas that serve as sources of replenishment, can potentially compensate for recruitment and ecosystem overfishing and enhance fishery yields for some coastal stocks. The efficacy of refugia in fisheries management is virtually untested, despite the existence of many marine parks and reserves. Evidence from existing marine reserves indicates that increased abundance, individual size, reproductive output, and species diversity occurred in a variety of marine species in refuges of various sizes, shapes, and histories in communities ranging from coral reefs to temperate kelp forests. Fishery yield enhancement in areas surrounding refuges occurred in the few studies where yields were examined. The export of propagules required to enhance fisheries in areas surrounding refugia adds a level of complexity to the design of fishery refugia beyond that of terrestrial reserves. Fishery refugia design should consider species life histories, oceanographic regimes, habitat quality, a...

Applications of marine refugia to coastal fisheries management

We have identified benthic recruitment habitats and nursery grounds of the American lobster Homarus americanus Milne Edwards in the coastal Gulf of Maine, USA, by systematically censusing subtidal sediment, cobble, and ledge substrata. We distinguish lobsters between settlement size (5 mm carapace length (CL)) to ca 40 mm CL as the 'early benthic phase' (EBP) because they are ecologically and behaviorally distinct from larger lobsters EBP lobsters are cryptic and apparently restricted to shelter-providing habitats (primarily cobble substratum) in coastal Gulf of Maine. In these habitats we found average population densities of EBP lobsters as high as 6.9 m-2 EBP lobsters were virtually absent from ledge and sedimentary substrata devoid of vegetation although larger lobsters are commonly found there. It is possible that the requirement for shelter-providing substrata by this life phase creates a natural demographic 'bottleneck' to benthic recruitment for the species. Prime cobble recruitment habitat is relatively rare and comprises ca 11 % of the 60.2 km of shoreline at our study area in midcoast Maine. If this low availability of cobble exists throughout the Gulf of Maine, as other studies indicate, it could limit lobster production potential. We verified the geographic extent of recruitment to cobble habitats censused in 3 of 4 regions spanning ca 300 km of the coastal Gulf of Maine (from Nahant, Massachusetts to Swans Island, Maine). Early benthic phase lobsters were absent from cobble censused in the northeastern extreme of our survey (Swans Island). This pattern is consistent with earlier speculation that relatively cool water temperatures may limit larval settlement in this region.

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Recruitment Habitats and Nursery Grounds of the American Lobster Homarus Americanus: A Demographic Bottleneck?

Chapter 10 – Control of Growth and Reproduction

A total of 2139 ovigerous lobsters, Homarus americanus, were tagged and egg development recorded off Grand Manan, eastern Canada, during 1982–83. Recaptures during August 1982 to January 1984 totaled 1877, representing 1046 individuals including 457 that were captured 2–10 times. The single recapture data indicate that the majority (75%) of the lobsters moved  20 km with recaptures in shallow (  200 m) water during winter–spring. Many ovigerous females returned to the Grand Manan area the following summer. A few (7%) moved north > 30 km into the Bay of Fundy and south as much as 322 km along the c...

Migratory Movements of Ovigerous Lobsters, Homarus americanus, Tagged off Grand Manan, Eastern Canada

We used a coupled physical–biological model to examine potential distances between hatching and settlement locations for lobsters in the Gulf of Maine. The physical model is based on a finite-element mesh and climatological averages of the seasonally evolving temperature and density fields. Larval trajectories from coastal and offshore hatching sites (21–224 m deep) were calculated for early, middle and late-season hatching by coupling temperature-dependent development rates and depth (the biological model) to the circulation. Model results showed large spatial differences in larval development times (from 18 to 38 days) and distances transported (19–280 km) for the early hatch. Development time and transport decreased markedly by mid-season at most sites, but strong spatial differences persisted. The eastern Maine coast appears to experience stronger removal and less resupply of larvae than other regions, consistent with observed lower recruitment. Inverse solutions of the model for larvae arriving in mid-coastal Maine indicate that they originate from a broad section of the eastern coast ‘upstream’, with those nearest the shoreline generally travelling the shortest distances. The postlarval stage is neustonic (living near the surface), and a simple inverse model demonstrates that a diurnal coastal sea breeze can contribute substantially to inshore movement during this final planktonic stage. Thus, offshore reproduction may be linked to inshore recruitment.

Modelling the transport of lobster (Homarus americanus) larvae and postlarvae in the Gulf of Maine

The relative abundance of berried female lobsters, Homarus americanus, and their contribution to total egg production in various areas of the Bay of Fundy and off southwestern Nova Scotia are estimated from sampling commercial and research cruise catches from traps. Concentrations of berried females occurred on Browns Bank, Georges Bank, and the New Brunswick side of the Bay of Fundy. To a lesser extent, berried females occurred in the coastal areas of southwestern Nova Scotia. Using a range of mortality values, a variety of population sizes were estimated from 1983 landings from which relative egg production values were calculated for each area. Lobsters from coastal waters of southwestern Nova Scotia combined with the Bay of Fundy were estimated to produce between 23 and 53% and those from the offshore Brown and eastern Georges Banks to produce between 47 and 77% of the region's total egg production. The results suggest that lobsters in each area are capable of producing large numbers of eggs. Where the...

D. S. Pezzack

Papers

Relative Egg Production and Abundance of Berried Lobsters, Homarus americanus, in the Bay of Fundy and off Southwestern Nova Scotia