Protection from fishing improves body growth of an exploited species.

Hunting and fishing are often size-selective, which favours slow body growth. In addition, fast growth rate has been shown to be positively correlated with behavioural traits that increase encounter rates and catchability in passive fishing gears such as baited traps. This harvest-induced selection should be effectively eliminated in no-take marine-protected areas (MPAs) unless strong density dependence results in reduced growth rates. We compared body growth of European lobster (Homarus gammarus) between three MPAs and three fished areas. After 14 years of protection from intensive, size-selective lobster fisheries, the densities in MPAs have increased considerably, and we demonstrate that females moult more frequently and grow more during each moult in the MPAs. A similar, but weaker pattern was evident for males. This study suggests that MPAs can shield a wild population from slow-growth selection, which can explain the rapid recovery of size structure following implementation. If slow-growth selection is a widespread phenomenon in fisheries, the effectiveness of MPAs as a management tool can be higher than currently anticipated.

Technological creep masks continued decline in a lobster (Homarus gammarus) fishery over a century.

Fishery-dependent data are frequently used to inform management decisions. However, inferences about stock development based on commercial data such as Catch-Per-Unit-Effort (CPUE) can be severely biased due to a phenomenon known as technological creep, where fishing technology improves over time. Here we show how trap improvement over nine decades has driven technological creep in a European lobster (Homarus gammarus) fishery. We combined fishing data, experimental fishing with contemporary and older trap types, and information on depletion effects during fishing seasons. The resulting standardized CPUE time series indicates a 92% decline in lobster abundance between 1928 and 2019 compared to 70% if technological creep is not corrected for. Differences are most pronounced within the last 40 years when the most substantial shift in gear technology occurred: an uncorrected CPUE index suggests an 8% increase in lobster abundance during this period, while the corrected CPUE index declined by 57%. We conclude that technological creep has masked a continuous stock decline, particularly in recent decades and largely driven by the shift from one- to two-chambered traps, as well as the ability of newer trap designs to capture larger lobsters. Our study confirms the importance of adequate standardization, including technological development, when using fishery dependent CPUE for monitoring and management of data-limited fisheries.

Fishing pressure impacts the abundance gradient of European lobsters across the borders of a newly established marine protected area.

Marine protected areas (MPAs) are considered viable fisheries management tools due to their potential benefits of adult spillover and recruitment subsidy to nearby fisheries. However, before-after control-impact studies that explore the biological and fishery effects of MPAs to surrounding fisheries are scarce. We present results from a fine-scale spatial gradient study conducted before and after the implementation of a 5 km2 lobster MPA in southern Norway. A significant nonlinear response in lobster abundance, estimated as catch-per-unit-effort (CPUE) from experimental fishing, was detected within 2 years of protection. After 4 years, CPUE values inside the MPA had increased by a magnitude of 2.6 compared to before-protection values. CPUE showed a significant nonlinear decline from the centre of the MPA, with a depression immediately outside the border and a plateau in fished areas. Overall fishing pressure almost doubled over the course of the study. The highest increase in fishing pressure (by a magnitude of 3) was recorded within 1 km of the MPA border, providing a plausible cause for the depression in CPUE. Taken together, these results demonstrate the need to regulate fishing pressure in surrounding areas when MPAs are implemented as fishery management tools.

Conservation, spillover and gene flow within a network of Northern European marine protected areas.

To ensure that marine protected areas (MPAs) benefit conservation and fisheries, the effectiveness of MPA designs has to be evaluated in field studies. Using an interdisciplinary approach, we empirically assessed the design of a network of northern MPAs where fishing for European lobster (Homarusgammarus) is prohibited. First, we demonstrate a high level of residency and survival (50%) for almost a year (363 days) within MPAs, despite small MPA sizes (0.5-1 km(2)). Second, we demonstrate limited export (4.7%) of lobsters tagged within MPAs (N = 1810) to neighbouring fished areas, over a median distance of 1.6 km out to maximum 21 km away from MPA centres. In comparison, median movement distance of lobsters recaptured within MPAs was 164 m, and recapture rate was high (40%). Third, we demonstrate a high level of gene flow within the study region, with an estimated F ST of less than 0.0001 over a ≈ 400 km coastline. Thus, the restricted movement of older life stages, combined with a high level of gene flow suggests that connectivity is primarily driven by larval drift. Larval export from the MPAs can most likely affect areas far beyond their borders. Our findings are of high importance for the design of MPA networks for sedentary species with pelagic early life stages.

Lobster and cod benefit from small-scale northern marine protected areas: inference from an empirical before-after control-impact study.

Marine protected areas (MPAs) are increasingly implemented as tools to conserve and manage fisheries and target species. Because there are opportunity costs to conservation, there is a need for science-based assessment of MPAs. Here, we present one of the northernmost documentations of MPA effects to date, demonstrated by a replicated before-after control-impact (BACI) approach. In 2006, MPAs were implemented along the Norwegian Skagerrak coast offering complete protection to shellfish and partial protection to fish. By 2010, European lobster (Homarus gammarus) catch-per-unit-effort (CPUE) had increased by 245 per cent in MPAs, whereas CPUE in control areas had increased by 87 per cent. Mean size of lobsters increased by 13 per cent in MPAs, whereas increase in control areas was negligible. Furthermore, MPA-responses and population development in control areas varied significantly among regions. This illustrates the importance of a replicated BACI design for reaching robust conclusions and management decisions. Partial protection of Atlantic cod (Gadus morhua) was followed by an increase in population density and body size compared with control areas. By 2010, MPA cod were on average 5 cm longer than in any of the control areas. MPAs can be useful management tools in rebuilding and conserving portions of depleted lobster populations in northern temperate waters, and even for a mobile temperate fish species such as the Atlantic cod.

Total catch of a red-listed marine species is an order of magnitude higher than official data.

Accurate information on total catch and effort is essential for successful fisheries management. Officially reported landings, however, may be underestimates of total catch in many fisheries. We investigated the fishery for the nationally red-listed European lobster (Homarus gammarus) in south-eastern Norway. Probability-based strip transect surveys were used to count buoys in the study area in combination with catch per unit effort data obtained independently from volunteer catch diaries, phone interviews, and questionnaires. We estimate that recreational catch accounts for 65% of total catch in the study area. Moreover, our results indicate that only a small proportion (24%) of lobsters landed commercially were sold through the legal market and documented. Total estimated lobster catch was nearly 14 times higher than reported officially. Our study highlights the need for adequate catch monitoring and data collection efforts in coastal areas, presents a clear warning to resource managers that illegal, unreported and unregulated (IUU) fisheries in coastal areas should not be ignored, and shows the potential impact of recreational fisheries.