Browsing by Subject "Rock lobster"
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- ItemOpen AccessEffects of protection and environmental factors on rock lobster, abalone, and giant periwinkle abundances in the Table Mountain National Park Marine Protected Area(2022) Gardner, Kathryn; Attwood, Colin; Kock, AlisonThe Table Mountain National Park Marine Protected Area (TMNP-MPA) was established in 2004 to restore and protect the Cape Peninsula's biodiversity, including the populations of exploited macro-invertebrate species. Scientific publications on MPAs support the idea that biodiversity protection is well served by MPAs, particularly no-take MPAs. Focusing on west coast rock lobster, abalone and giant periwinkle, historically the three most important invertebrate resources of the region, this study assesses the effectiveness of spatial regulations in the TMNP-MPA. Three comprehensive peninsula-wide SCUBA surveys were conducted in 2000, 2003 and 2019. Patterns in the abundance of the three species were analyzed using generalized-linear models (GLM) to explore the effects of the TMNP-MPA and no-take zones within, whilst accounting for habitat, depth, species interactions, and the physical protection offered by False Bay. Overall, the rock lobster abundance around the Cape Peninsula decreased since the implementation of the TMNP-MPA, however, to a lesser degree than the dramatic overall decline of the rock lobster population in South Africa over this time. This decrease is possibly due to increased illegal harvesting of adults and juveniles and increased predation from recovering fish populations within TMNP-MPA. However, rock lobster abundance did respond positively to the length of protection in no-take zones, suggesting that the enforcement of no-take zones within the MPA was effective. The beneficial effects of the no-take zones are likely insufficient to compensate for increased harvesting in adjacent areas within the MPA but prevented a greater decline in rock lobster. No change in abalone abundance was detected over the years in the TMNP-MPA or within no-take protected zones. The regional abalone population has declined drastically over a similar period due to poaching. Effective policing has likely prevented the abalone within the MPA from following suit. Giant periwinkle abundance increased since the establishment of TMNP-MPA. However, it is unknown if this pattern reflects the regional giant periwinkle population, so it cannot be determined if the increase is a direct result of the MPA. However, the giant periwinkle abundance had not benefited from the no-take zones, suggesting general harvest restrictions in TMNP-MPA are affording them sufficient protection, or that the greater population is increasing. A combination of environmental factors, such as warmer water temperatures and reduced nutrients, could explain the decreased abundance of rock lobster in False Bay, compared to those along the Peninsula's west coast. Predation by rock lobster could explain the opposite pattern found in both the giant periwinkle and abalone that were more common in False Bay. Expected abundance patterns based on the habitat preferences of each species, associated with water depth, the presence of sand, and kelp and urchin density were found. The creation of the TMNP-MPA, with its many and varied no-take and harvest zones provided an excellent opportunity to test the effectiveness of no-take spatial protection in a complex marine community and in the vicinity of a heavily exploited coastal zone near a metropolitan setting. This is especially valuable for macro-invertebrates, which are not commonly the focus of MPA studies in South Africa. This study supports the use of MPAs as a protection measure for overexploited macro-invertebrates. The extent of the success of this protection is evident by way of comparison with the magnitude of declines elsewhere. As both rock lobster and abalone fisheries are heavily plagued by poaching, the impact of no-take zones and the enhanced policing brought by the TMNP-MPA as a whole, likely helped to buffer the declines of rock lobster and abalone, respectively.
- ItemRestrictedFurther updated West Coast rock lobster operating models for super-areas A1+2 and A8+(2011) Johnston, Susan J; Butterworth, Doug SAt the previous SWG meeting (23 March 2011) results of updated operating models for all five super-areas of the west coast rock lobster resource were presented (Johnston and Butterworth 2011). The SWG requested that two of the operating models be re-run following discussions at the meeting. These re-runs are: Area 1+2: Re-run the model with the constraint that all estimable recruitment parameters must be 1.0, when expressed as a proportion of the pristine recruitment. Area 8+: Re-run the model with updated values for both the trapboat and hoopnet CPUE series. Glazer and Butterworth (2011a,b) report updated CPUE values. These values have been updated to include Area 8 sub-areas and to take into account Areas 10-14 as recommended.
- ItemOpen AccessRock lobster scientific working group agreed recreational catch estimates(2010) Johnston, Susan J; Butterworth, Doug SIn 2009, Anchor (the service provider responsible for the telephone survey for 2008/09) reported that there was an error in the method used for drawing the random numbers to be used to select permit holders to call for the telephone surveys which are conducted every two weeks (see Johnston and Butterworth 2009 for details). The correct method would be to draw the random numbers from all currently registered permit holders, i.e. those that had bought permits from the start of the season to the then current date. What had occurred (incorrectly) however, was that random telephone numbers were being drawn only from permit holders who had bought permits in the previous two weeks.
- ItemOpen AccessSummary of suggested baseline options for rock lobster TAC recommendations for the Tristan da Cunha group of islands (i.e. had no oil spill event occurred in 2011)(2011) Johnston, Susan J; Butterworth, Doug SThis document presents four options for what would have been the basis for recommending TACs for the rock lobster resources at the four Tristan islands had the oil (and soya) spill event not occurred. Though pertinent to the coming season, the rationale for a number of these options is also linked to longer-term optimal sustainability considerations. The longer-term implications of the differences between these options are illustrated by providing resource projections based on the most recent age-structured model assessment of these resources.
- ItemOpen AccessUpdated analyses of the Fisheries Independent Monitoring Survey data of the Rock Lobster resource of South Africa to include the 2017/18 season(2018-07) Brandão, Anabela; Butterworth, Doug SAnalyses of FIMS data are updated to include data for the 2016/17 and 2017/18 seasons. Results show an increase from the last season’s index for the FIMS relative abundance indices in the Cape Point Zone, although this increase follows from the lowest observed abundance index for this area. A drop from the last season’s index of abundance is seen for Dassen Island, Saldanha Bay and Lambert’s Bay Zones. The percentage of females compared to the last season has decreased in the Cape Point Zone and increased in the Dassen Island, Saldanha Bay and Lambert’s Bay Zones.