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41.
The shared Torres Strait rock lobster (Panulirus ornatus) fishery provides important income for commercial and traditional fishers in Australia and Papua New Guinea. The lobster stock is first fished in Torres Strait by divers from both countries and then becomes vulnerable to Australian prawn trawlers, followed by Papua New Guinea trawlers during its annual breeding migration. Lobster catch sharing arrangements are governed by the Torres Strait Treaty ratified in 1985, but the sequential trawling of breeding lobsters has been controlled by bilateral agreements. A trawl ban was implemented in 1984 in both countries to conserve the breeding stock, but some trawling has been conducted in the Gulf of Papua since then and there is renewed interest in Papua New Guinea to resume trawling. To evaluate the impact of trawling migratory breeding lobsters on the lobster fishery, a model that combines a cohort depletion model with a stock recruitment relationship was developed in this study. The model showed that when the fishery is fully or over‐exploited by the dive fishery, trawling breeding lobsters would reduce both the spawning stock and the total catch of the fishery. The reduction in catch would increase with increasing fishing mortality. If trawling occurred on the Papua New Guinea side only, a redistribution of catch between Australia and Papua New Guinea would result in a small gain in catch for Papua New Guinea at the expense of the Australian dive fishery. But when fishing mortality reaches a certain level, any trawling in any country will incur catch loss to both countries. For the long‐term sustainability and maximum production of the fishery, regulations should be implemented in both countries under a co‐management scheme of a shared fish stock. 相似文献
42.
One of the aims of Mediterranean marine protected areas (MPAs) is to increase populations of exploited species, such as the European spiny lobster (Palinurus elephas), which is considered a key species for its commercial and ecological value. Monitoring of temporal patterns in abundance of early benthic stages of P. elephas indicated that predation may be higher inside the Medes Islands MPA relative to adjacent control sites. Tethering experiments were performed to test whether predation rates actually differed within and outside the MPA. Relative mortality of recently‐settled juveniles inside the MPA was much higher than in control sites in adjacent non‐protected areas. Treatments with and without shelter indicated that predation on recently‐settled juvenile spiny lobsters was moderated by the availability of suitable shelter. The decline or absence of fish predators in the fished area may be the reason why juvenile lobsters outside the MPA experience lower predation than within the MPA. 相似文献
43.
Louise Gendron 《新西兰海洋与淡水研究杂志》2013,47(3):661-674
In the mid 1990s, American lobster (Homarus americanus) from Canadian waters was considered overfished based on estimated levels of egg‐per‐recruit production (EPR). In 1997, the Department of Fisheries Oceans responded by adopting a goal of doubling the level of EPR from its 1996 level. In the Magdalen Islands (Quebec), results from a simulation model indicated that doubling EPR could be reached by increasing the minimum legal size (MLS) from 76 mm to 83 mm carapace length. This was done at a pace of 1 mm per year from 1997 to 2003. Following the increase of MLS, the size structure, mean size, and the abundance of ovigerous females improved significantly in the catches. However, levels of fishing effort are still very high. This could cause undesirable effects such as altering sex ratios and size structure of males, which could lead to sperm limitation, and reducing the contribution of multiple spawners to egg production, which could become an issue if egg quality is important. Consideration of these issues leads to the recommendation of a multidimensional approach to lobster conservation. 相似文献
44.
Since 2002, 5.3% of the Victorian coastal waters have been declared as Marine Protected Areas (MPAs). These are aimed at safeguarding important marine habitats and species, significant natural features, and areas of cultural heritage and aesthetic value. However, MPAs impact the fishery for southern rock lobster (Jasus edwardsii), as total allowable catches (TACs) were previously set to allow the biomass to recover to pre‐specified target levels. The model on which assessments and risk analyses are based is extended to include the impact of MPAs. The MPAs and the area open to fishing are modelled as subpopulations with different levels of mortality and consequently different density and population size‐structure. A range for the probability of a lobster moving from a MPA to the fished area from 0 to 15% is considered, based on the results of tagging studies. The reduction of biomass available to the commercial fishery because of the introduction of MPAs is estimated to be 8% and 16% (Western and Eastern Zones) respectively. The results of a risk assessment show that if the current TACs are maintained, the time to increase the biomass available to the commercial fishery by 50% would be delayed 5–9 years in the Western Zone and 1–4 years in the Eastern Zone because of the impact of displaced effort. In contrast, spawning biomass in the Eastern Zone is currently below the agreed limit reference point, and the introduction of MPAs would enhance the rate of recovery, although only marginally initially, faster than the absence of the MPAs. 相似文献
45.
The commercial fishery for Jasus lalandii, the South Africa West Coast rock lobster, began in the late 1800s and at its peak in the early 1950s yielded an annual catch of 18 000 t. Although this annual catch has dropped to only some 2000 t over recent years, the fishery remains South Africa's third most valuable for landed value. The primary reason for the low total allowable catch (TAC) over these recent years has been a marked drop in somatic growth rate that occurred at the end of the 1980s, for reasons that remain unexplained. A key problem in formulating TAC recommendations with longer‐term objectives in mind, has been uncertainties about likely future trends, particularly in somatic growth and recruitment. To address this problem, an “operational management procedure” (OMP) was adopted in 1997 and has twice been re‐evaluated and modified (in 2000 and 2003) in the light of further data and changing perceptions of resource dynamics. The history of this process is reviewed, concentrating on the most recent modification. In particular, a summary is given of the process by which the merits of alternative management procedures were evaluated over a range of important uncertainties about the dynamics of the resource. This summary includes a discussion of the key trade‐offs between resource rebuilding, future TAC trends and TAC variability, and the eventual choice that was made. The paper concludes by listing a number of lessons learnt concerning best practice for OMP development as this process evolved. 相似文献
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47.
The ornate rock lobster (Panulirus ornatus) is distributed across Torres Strait between Australia and Papua New Guinea and supports the most important commercial fishery to Islanders in the region. The long-term sustainability of the fishery is of importance not only to local island communities but also to the bilateral relationship between the two countries. In this paper, we developed an age-structured fishery model to assess the current stock status and estimate the long-term sustainable catch. The model was fitted to catch statistics and survey-based population estimates through a weighted maximum likelihood approach. Natural mortality was estimated at 0.732 yr−1, and fishing mortality ranged from 0.19 to 0.65 yr−1 from 1989 to 2005. The maximum sustainable yield was estimated at about 640 tonnes whole weight with a corresponding fishing mortality of 0.5 yr−1. A stock–recruitment model was established based on outputs of the stock assessment model. To obtain the maximum sustainable yield, spawning stock should be maintained at 120×104 lobsters. The lobster spawning stock has been fished down below this level twice since 1989, in 1999 and 2002, and was higher than this level in 2004 and 2005. These results suggest that the Torres Strait lobster stock is not over-fished and that the current harvest strategy is likely to maintain the stock at or above the level that would support the maximum sustainable yield if the current cap on fishing effort remains in place. 相似文献
48.
The Northern Zone rock lobster fishery of South Australia is expansive, covering an area of ∼207,000 km2. From 1970 to 2002 it was managed under input controls that relied heavily on restrictions to days-at-sea and size limits. In 2003, output controls in the form of individual transferable quotas with a total allowable commercial catch were also introduced. Fishery performance from 1980 to 2007 was analysed based on catch data and model outputs. Trends in catch and effort increased through the 1980s and 1990s while nominal catch rate remained relatively stable. However, from 1999 to 2003 catch decreased by 49% from 1001 to 503 ton and has remained at <500 ton since. Importantly, nominal effort did not decline comparatively, decreasing by only 12% from 1999 to 2007. Consequently, nominal catch rate decreased by 47.5% from 1.43 to 0.75 kg/potlift, over the same period. Logbook data revealed strong evidence of spatial expansion through the 1980s and 1990s which is likely to have masked declining lobster abundance and contributed to a “hyperstability” scenario in catch rates. It is suggested that increasing effective effort, driven by advances in fishing technology and vessel design, fuelled this expansion. Model outputs, which account for increases in effective effort, indicate that biomass has decreased by ∼68% since the 1980s. The results highlight the limitations associated with input controls in controlling effort during periods of spatial expansion. Further evidence from puerulus settlement data stresses the importance of conservative quotas for lobster fisheries where annual recruitment is low or highly sporadic. 相似文献
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Frances B. Michaelis 《新西兰海洋与淡水研究杂志》2013,47(4):613-628
The physical and chemical features of Pupu Springs (40 51’ S, 172° 46’ E), near Takaka, the largest cold springs in New Zealand and one of the largest in the world, were investigated by scuba diving. The springs have a maximum depth of 6.9 m and a mosaic of substrate types (bedrock, boulders, and gravel). The temperature of the springs water is constant at 11.7°C, water velocities are generally moderate to very strong (25–100 cm.s‐1), and average water discharge is about 9.6 m3.s‐1. Mean holding time for water in the springs is 4.4 min. The water is extremely clear, with a vertical extinction coefficient (log10) of 0.09. The springs water flows from an artesian basin in Arthur Marble and is low in dissolved oxygen. The water is rich in calcium (64 g.m‐3), with a high specific conductivity (65 mS.m‐1). Information on water temperature, discharge, and chemistry is provided for five other cold springs in New Zealand: Hamurana Springs, Rotorua; Otangaroa Springs, near Putaruru; Three Springs, near Fairlie; Western Springs, Auckland; and a spring at Lake Hayes, Queenstown. 相似文献