Site fidelity and along-shore range in Hector's dolphin, an endangered marine dolphin from New Zealand

Bräger, Stefan; Dawson, Stephen M.; Slooten, Elisabeth; Smith, Susan; Stone, Gregory S.; Yoshinaga, A.

doi:10.1016/s0006-3207(02)00124-6

Cited by 51 publications

(53 citation statements)

References 17 publications

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“…Similar numbers of sightings were made in the summer and winter aerial surveys, and the same individual dolphins have been sighted in the same areas in summer and winter (Bräger et al 2002). There is no evidence that dolphins leave the Banks Peninsula area during winter; instead their distribution becomes more dispersed.…”

Section: Discussionsupporting

confidence: 57%

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

Slooten¹,

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Dawson

2006

New Zealand Journal of Marine and Freshwater Research

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Aerial surveys of Hector's dolphins were carried out to evaluate the effectiveness of the Banks Peninsula Marine Mammal Sanctuary. In summer, the proportion of sightings inside the 4 nautical mile offshore boundary of the sanctuary was 79%. This dropped to just over 35% in winter. These estimates were used in a population viability analysis to determine whether the sanctuary needs to be extended to reduce dolphin bycatch to sustainable levels. We followed the standard procedure for setting limits on marine mammal bycatch in the United States to calculate a bycatch limit of 1.6 or 2.8 dolphins per year (depending on whether the sanctuary population is included). If the offshore boundary was extended to 15 nautical miles, the sanctuary would need to be extended alongshore north and south by more than 30 nautical miles to reduce bycatch to 2.8, or north and south by 60 nautical miles to reduce bycatch to 1.6 dolphins per year.

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Section: Discussionsupporting

confidence: 57%

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

Slooten¹,

Rayment

Dawson

2006

New Zealand Journal of Marine and Freshwater Research

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“…Hector's dolphins show strong site fidelity. Their home range extends for an average of 31 ± 2.43 (SE) km of coastline, and individuals are seen in the same area throughout the year and over many years (Bräger et al 2002). The movement rate between areas at this scale has been estimated at less than 1% of the population per year (Fletcher et al 2002).…”

Section: Methodsmentioning

confidence: 99%

“…In addition, more detailed mark-recapture work was carried out at Banks Peninsula and an adjacent area from Timaru to the Rakaia River mouth. These studies indicate that the movement rate is <1% of the population yr -1 at the scale of the 16 fishing areas used in the model (Bräger 1998, Bräger et al 2002, Martien et al 1999, Fletcher et al 2002. Movement was modelled stochastically, with the movement rate (0, 1 or 5% of the population for the sensitivity trials, 1% for all other analyses) used as the probability of each individual migrating from its original area to an adjacent area in any given year.…”

Section: Methodsmentioning

confidence: 99%

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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“…Our photo-ID protocols, including the criteria used for image quality, are described in detail by Slooten et al (1992) and Bräger et al (2002).…”

Section: Materialsand Methodsmentioning

confidence: 99%

Observations of Hector's dolphins (Cephalorhynchus hectori) associating with inshore fishing trawlers at Banks Peninsula, New Zealand

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Webster

2009

New Zealand Journal of Marine and Freshwater Research

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Fishing activities have the potential to alter the behaviour of cetaceans and pose a threat through bycatch. We present observations concerning the influence of inshore trawling on group size and behaviour of Hector's dolphins (Cephalorhynchus hectori) at Banks Peninsula, New Zealand, made during photo-ID surveys from 2003 to 2007. Aggregations of dolphins, typically involved in what we assumed to be foraging behaviour, were observed following small inshore trawlers yearround. Group size was larger for aggregations of dolphins following trawlers (mean ± SE = 22.9 ± 1.3, n = 83) than for non-trawler groups (3.7 ± 0.2, n = 439), and dolphins were typically in a more "excited" state, frequently exhibiting aerial and sexual behaviours. We suggest that trawlers increase the availability of prey for Hector's dolphins and hence foraging behind trawlers is an energetically favourable activity. However, following trawlers probably also increases the risk of being caught in trawl nets, compounding the threats faced by this endangered species.

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Site fidelity and along-shore range in Hector's dolphin, an endangered marine dolphin from New Zealand

Cited by 51 publications

References 17 publications

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

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

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

Observations of Hector's dolphins (Cephalorhynchus hectori) associating with inshore fishing trawlers at Banks Peninsula, New Zealand

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Site fidelity and along-shore range in Hector's dolphin, an endangered marine dolphin from New Zealand

Cited by 51 publications

References 17 publications

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

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

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

Observations of Hector's dolphins (Cephalorhynchus hectori) associating with inshore fishing trawlers at Banks Peninsula, New Zealand

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