Offshore distribution of Hector's dolphins at Banks Peninsula, New Zealand: Is the Banks Peninsula Marine Mammal sanctuary large enough?

Slooten, Elisabeth; Rayment, William; Dawson, Steve

doi:10.1080/00288330.2006.9517425

Cited by 28 publications

(26 citation statements)

References 23 publications

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“…The proportion of Hector's dolphin groups sighted inside the 4 nautical mile sanctuary boundary was 78.6% in summer and 35.1% in winter (Slooten et al 2006b). Adding Hector's dolphins found inside Area 12 but north and south of the sanctuary boundaries, led to an estimate of 50.8% of the population being outside the sanctuary in summer and 78% being outside the sanctuary in winter (Slooten et al 2006b). The average exposure of dolphins to gillnets was based on these distribution data as well as the relative amount of fishing in summer and winter (Slooten et al 2006b).…”

Section: Methodsmentioning

confidence: 99%

“…Adding Hector's dolphins found inside Area 12 but north and south of the sanctuary boundaries, led to an estimate of 50.8% of the population being outside the sanctuary in summer and 78% being outside the sanctuary in winter (Slooten et al 2006b). The average exposure of dolphins to gillnets was based on these distribution data as well as the relative amount of fishing in summer and winter (Slooten et al 2006b). Starr & Langley (2000) estimated that 71% of the gillnet fishing effort (in total metres of net used) occurs in spring and summer (October to March) and the remaining 29% in autumn and winter (April to September).…”

Section: Methodsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

“…The effectiveness of Option A is based on data on the proportion of the population found inside and outside the Banks Peninsula Marine Mammal Sanctuary, estimated using a series of linetransect surveys , Rayment et al 2006, Slooten et al 2006b). The proportion of Hector's dolphin groups sighted inside the 4 nautical mile sanctuary boundary was 78.6% in summer and 35.1% in winter (Slooten et al 2006b). Adding Hector's dolphins found inside Area 12 but north and south of the sanctuary boundaries, led to an estimate of 50.8% of the population being outside the sanctuary in summer and 78% being outside the sanctuary in winter (Slooten et al 2006b).…”

Section: Methodsmentioning

confidence: 99%

“…Starr & Langley (2000) estimated that 71% of the gillnet fishing effort (in total metres of net used) occurs in spring and summer (October to March) and the remaining 29% in autumn and winter (April to September). The proportion of dolphins exposed to gillnet fisheries in any given year was therefore estimated as a weighted average, multiplying the proportion of dolphins found outside the sanctuary and the proportion of fishing effort for each season to estimate an average exposure to gillnets of 58.7% (see Slooten et al 2006b for more details). This is an optimistic estimate of the level of protection, as there have been continued dolphin catches inside the sanctuary (DOC & MFish 2007) partly because recreational gillnetting is still allowed inside the sanctuary for 8 mo of the year and partly due to illegal gillnetting within the sanctuary.…”

Section: Methodsmentioning

confidence: 99%

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Conservation management in the face of uncertainty: effectiveness of four options for managing Hectors dolphin bycatch

Slooten

2007

Endang. Species Res.

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New Zealand's endemic Hector's dolphins Cephalorhynchus hectori overlap with gillnet and trawl fisheries throughout their geographic range. The catch rate in commercial gillnets has been estimated using independent observers. No quantitative estimates are available for bycatch in recreational gillnets or trawl fisheries. The catch rate (per dolphin, per km of gillnet, per year) in commercial gillnets was used in a population viability analysis to estimate past and future population sizes. Total population size today (7873, coefficient of variation [CV] 0.16) was estimated at 27% of population size in 1970 (29316, CV 0.16), before a major expansion of commercial gillnetting. The species matches IUCN criteria for 'endangered'. The North Island subspecies matches criteria for 'critically endangered'. Current management, which includes 2 protected areas, is not sufficient to halt population declines. Hector's dolphin populations are predicted to continue declining to 5475 (CV 0.20) by 2050. Creating 4 strategically placed protected areas would allow population recovery towards 1970 levels, with an estimated 47% probability of reaching 50% of 1970 population size by 2050 (proportion of 5000 model runs in which final population size was at or above this reference level). Reducing fisheries mortality to levels approaching zero shows the strongest promise of meeting national and international guidelines for managing dolphin bycatch, with a 59% probability of reaching 50% of 1970 population size by 2050.

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Section: Methodsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

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Conservation management in the face of uncertainty: effectiveness of four options for managing Hectors dolphin bycatch

Slooten

2007

Endang. Species Res.

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Assessing the effectiveness of conservation management decisions: likely effects of new protection measures for Hector's dolphin (Cephalorhynchus hectori)

Slooten

Dawson

2009

Aquatic Conservation

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ABSTRACT1. Fisheries bycatch affects many species of marine mammals, seabirds, turtles and other marine animals. 2. New Zealand's endemic Hector's dolphins overlap with gillnet and trawl fisheries throughout their geographic range. The species is listed as Endangered by the IUCN. In addition, the North Island subspecies has been listed as Critically Endangered.3. Estimates of catch rates in commercial gillnets from an observer programme (there are no quantitative estimates of bycatch by amateur gillnetters or in trawl fisheries) were used in a simple population viability analysis to predict the impact of this fishery under three scenarios: Option (A) status-quo management, (B) new regulations announced by the Minister of Fisheries in 2008 and (C) total protection.4. Uncertainty in estimates of population size and growth rate, number of dolphins caught and other model inputs are explicitly included in the analysis. Sensitivity analyses are carried out to examine the effect of variation in catch rate and the extent to which fishing effort is removed from protected areas but displaced to unprotected areas.5. These methods are applicable to many other situations in which animals are removed from populations, whether deliberately (e.g. fishing) or not (e.g. bycatch).6. The current Hector's dolphin population is clearly depleted, at an estimated 27% of the 1970 population. Population projections to 2050 under Options A and B predict that the total population is likely to continue declining. In the case of Option B this is driven mainly by continuing bycatch due to the much weaker protection measures on the South Island west coast.7. Without fishing mortality (Option C) all populations are projected to increase, with the total population approximately doubling by 2050 and reaching half of its 1970 population size in just under 40 years.

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Spatial behavioural response of coastal bottlenose dolphins to habitat disturbance in southern Brazil

Agrelo

Daura‐Jorge

Bezamat

et al. 2019

Aquatic Conservation

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A small population of coastal bottlenose dolphins (Tursiops truncatus gephyreus) inhabits the inland waters of Laguna, southern Brazil. A subset of this population interacts with artisanal fishermen. This specialized foraging tactic structures dolphin society into ‘cooperatives' (participants of the interaction) and ‘non‐cooperatives' (non‐participants). Between 2012 and 2015, a bridge was constructed in Laguna over an important core area for dolphins. Photo‐identification and georeferenced data collected on boat surveys, conducted both before and during bridge construction, were used to evaluate changes in both ‘cooperative' and ‘non‐cooperative' dolphin distribution. Changes in dolphin distribution were analysed with kernel densities and hurdle models. A grid of 120 cells of area 1 km2 was used to model dolphin distribution, and the minimum distance from the grid cell centre to the bridge and to the area of gillnet use were defined as explanatory variables of human activities. Habitat descriptors (depth and distance) from the lagoon margin were also considered in the model procedure. Dolphin distribution patterns shifted between periods. A core area used by ‘non‐cooperative' dolphins near the bridge construction works disappeared. The effects of habitat descriptor and anthropogenic activity on dolphin distribution also differed between periods. Before bridge construction, the abundance of ‘non‐cooperative' dolphin was higher close to the bridge area (p < 0.05). During bridge construction, the presence of ‘cooperative' and ‘non‐cooperative' dolphins decreased significantly with the distance from gillnet fishing activity (p < 0.01 and p < 0.001 respectively). This study highlights the importance of accounting for individual variations in response when assessing the effects of a habitat disturbance, or when implementing conservation plans.

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Offshore distribution of Hector's dolphins at Banks Peninsula, New Zealand: Is the Banks Peninsula Marine Mammal sanctuary large enough?

Cited by 28 publications

References 23 publications

Conservation management in the face of uncertainty: effectiveness of four options for managing Hectors dolphin bycatch

Conservation management in the face of uncertainty: effectiveness of four options for managing Hectors dolphin bycatch

Assessing the effectiveness of conservation management decisions: likely effects of new protection measures for Hector's dolphin (Cephalorhynchus hectori)

Spatial behavioural response of coastal bottlenose dolphins to habitat disturbance in southern Brazil

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Offshore distribution of Hector's dolphins at Banks Peninsula, New Zealand: Is the Banks Peninsula Marine Mammal sanctuary large enough?

Cited by 28 publications

References 23 publications

Conservation management in the face of uncertainty: effectiveness of four options for managing Hectors dolphin bycatch

Conservation management in the face of uncertainty: effectiveness of four options for managing Hectors dolphin bycatch

Assessing the effectiveness of conservation management decisions: likely effects of new protection measures for Hector's dolphin (Cephalorhynchus hectori)

Spatial behavioural response of coastal bottlenose dolphins to habitat disturbance in southern Brazil

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Conservation management in the face of uncertainty: effectiveness of four options for managing Hectors dolphin bycatch

Conservation management in the face of uncertainty: effectiveness of four options for managing Hectors dolphin bycatch