Elisabeth Slooten

Pingers, porpoises and power: Uncertainties with using pingers to reduce bycatch of small cetaceans

Incidental mortality in gillnets is probably the most serious global threat to dolphin and porpoise populations. In 1994, a well-designed study demonstrated a 92% reduction in bycatch of harbour porpoises in sink gillnets equipped with acoustic pingers. This result has not yet been fully replicated; in the New Hampshire area where the experiment was conducted or elsewhere. Statistical power analyses indicate that such studies are feasible only in areas of high entanglement rate. Currently unanswered research questions include whether the 1994 results can be replicated, whether habituation might decrease effectiveness over time, and what the mechanism of deterrence is. Practical constraints include the size, cost and battery life of current pingers, and whether their use could be monitored cost-effectively. From a management perspective, even if the effectiveness of pingers is confirmed, widespread incorporation of them into gillnets may not alone be sufficient to meet the requirements of the US Marine Mammal Protection Act. For this reason scientists, managers and fishers must continue to explore other options, including time/area closures and encouragement of more selective fishing methods.

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

Abstract To document site fidelity and the alongshore range of individual Hectors dolphins we analysed sightings of 32 photographically identified dolphins, each seen ⩾10 times at Banks Peninsula, New Zealand, between 1985 and 1997. The furthest two sightings of an individual were 106 km apart. All other individuals ranged over less than 60 km ( x =31.0 km, SE=2.43) of coastline. Gender did not significantly influence alongshore range (female x =30.4 km, SE =3.21, n =18; male x =27.4 km, SE=5.68, n =5). Site fidelity was high: for example, on average, individuals were seen in Akaroa Harbour for about two thirds of the years they were known to be alive. These data suggest that impacts on Hectors dolphins are most appropriately managed on a small spatial scale.

Behavior of Hector's Dolphin: Classifying Behavior by Sequence Analysis

Behavior sequence analysis was used to classify behavior patterns of Hectors dolphin ( Cephalorhynchus hectori ) into five categories; feeding, sexual, aggressive, play, and aerial. Feeding behaviors were among the most closely associated behaviors, and were negatively associated with most other behaviors. Bite was closely associated with other apparently aggressive behaviors like tailsplash and chase. Copulations and possible copulations were associated with other behaviors one might have intuitively classified as sexual or social (e.g., belly present, penis out, and body contact). Aerial behaviors were most strongly associated with sexual and aggressive behaviors. Of the two play behaviors, play with weed was most strongly associated with feeding, and bubbleblow was most strongly associated with aggressive and aerial behaviors. I investigated the relationship between the sexual behavior category and social context. The rate of sexual behaviors per individual was highest in groups of 11–15 dolphins and tended to increase after groups came together.

Population viability analysis for Hector's dolphin (Cephalorhynchus hectori): A stochastic population model for local populations

Abstract Mortality of Hectors dolphin (Cephalorhynchus hectori) in gill‐net fisheries is a threat to local populations throughout its range. This population viability analysis extends previous work by exploring a wider range of fishing levels and population growth rates, by incorporating year‐to‐year and environmental variability and by reporting results for smaller population units. Ten of the 16 populations are likely to continue to decline, five are indefinite, and one is likely to increase. All populations subjected to high fishing effort are declining. The only population predicted to increase is partly protected by a marine mammal sanctuary (created in 1988) which reduces the amount of gill‐net fishing. Conservation measures are most urgently needed for the highly threatened North Island population, in particular the dolphins at the northern and southern end of this range.

Growth and reproduction of female New Zealand sea lions

Abstract A sample of 834 female New Zealand sea lions (Phocarctos hookeri), which were aged and measured, was obtained between 1998 and 2001. In addition, the reproductive histories of 505 marked females from the Auckland Islands were recorded from 1998 to 2005. These data sets were used to investigate growth and reproductive rates. Length and weight ranged from 134 to 197 cm and 49 to 156 kg, respectively. A Gompertz growth model best described growth and predicted that females attained 90% of asymptotic length (161.7 cm) and weight (112.0) at ages 4 and 11 years, respectively. No significant differences were found in growth rates among years, nor between the 2 major breeding colonies in the Auckland Islands. Females reproduced between the ages of 3 and 26 years, with evidence of reproductive senescence starting at age 23 years. Although females up to age 28 years were observed, no females over 26 years were recorded as reproductive. Age-specific reproductive rate p(x) increased rapidly between ages 3 and 7 years, reached a plateau between ages 7 and 23 years, and then declined rapidly after age 23 years. Mean observed reproductive rate was p(x)3–28  =  0.67 (SE  =  0.01). This is the 1st robust estimate of reproductive rate for this species, is consistent with rates reported for other sea lions, and is considerably lower than assumed rates used in recent population modeling for this species. This calls into question the current method for estimating levels of sustainable bycatch. Low growth and reproductive rates are consistent with a population that is occupying a marginal foraging environment. These factors, along with a recent significant decline in pup production, suggest that current management is insufficient to ensure population stasis, let alone meet the statutory goal of recovery.

Modelling Survival of Hector's Dolphins around Banks Peninsula, New Zealand

In 1988, a marine mammal sanctuary was established around Banks Peninsula to reduce Hectors dolphin entanglement in commercial and recreational gill nets. We describe the application of a multistate mark-recapture model to data from photographic identification surveys to determine the effect of the sanctuary on dolphin survival rates. The model allows sightings to occur in three geographic strata with free movement between strata. Although we found evidence of both area and time effects on sighting probabilities we found no evidence that survival rates depended on area or time. Thus, there was no evidence that dolphin survival rates increased following establishment of the sanctuary. However, power of this test is shown to be low.

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

Abstract Aerial surveys of Hectors 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.

Measuring body length of male sperm whales from their clicks: The relationship between inter-pulse intervals and photogrammetrically measured lengths

Sperm whales (Physeter macrocephalus) emit short, broadband clicks which often include multiple pulses. The time interval between these pulses [inter-pulse interval (IPI)] represents the two-way time for a pulse to travel between the air sacs located at either end of the sperm whales head. The IPI therefore, is a proxy of head length which, using an allometric relationship, can be used to estimate total body length. Previous studies relating IPI to an independent measure of length have relied on very small sample sizes and manual techniques for measuring IPI. Sound recordings and digital stereo photogrammetric measurements of 21 individuals were made off Kaikoura, New Zealand, and, in addition, archived recordings of whales measured with a previous photogrammetric system were reanalyzed to obtain a total sample size of 33 individuals. IPIs were measured automatically via cepstral analysis implemented via a software plug-in for pamguard, an open-source software package for passive acoustic monitoring. IPI measurements were highly consistent within individuals (mean CV=0.63%). The new regression relationship relating IPI (I) and total length (T) was found to be T=1.258I+5.736 (r(2)=0.77, p<0.001). This new regression provides a better fit than previous studies of large (> 11 m) sperm whales.

Hector's dolphin risk assessments: old and new analyses show consistent results

Abstract We review results of previous research and present new estimates of Hectors dolphin (Cephalorhynchus hectori) bycatch. Before 2008, an estimated total of 110–150 individuals were caught annually, with 35–46 caught off the east coast South Island (ECSI). We estimate that 23 Hectors dolphins were caught off ECSI during 1 May 2009–30 April 2010 (CV 0.21) based on fisheries observer data. This confirms results from risk analyses, indicating continued overlap between dolphins and fisheries. There is a high level of consistency among different risk assessments, despite large differences in model structure and parameterization. For example, without fisheries mortality Hectors dolphin populations could recover from 7873 (CV 0.16) today to around 15,000 individuals in the next 50 years (Schaefer model estimate 15,411; CV 0.16; Bayesian model 14,650; range 12,313–19,250). All risk analyses indicate that populations have declined substantially due to fisheries mortality and recovery is unlikely under the current protection measures.

Designing a mark-recapture study to allow for local emigration

In using a population projection model to help manage the conservation of along-lived species, we usually need a reliable estimate of adult survival. Mark-recapture studies are often used to estimate survival, and typically require the assumption that there is no permanent emigration from the study area. We consider how such a study might be extended to allow for local emigration, that is, movement of individuals into an area peripheral to the study area. In particular, we focus on the question as to how much field effort is required in this peripheral area in order to obtain sufficiently precise estimates of both the survival probability and the probability of local emigration. We consider the use of multi-state, mark-recapture models as a means of providing these estimates and show how to assess the precision of a potential study design by calculating the expected confidence limits associated with the resulting estimates. We considera range of design scenarios for the situation that motivated this work, involving a population of Hector’s dolphins in New Zealand. For this case, it appears that there is little gain in precision once a capture probability of 0.4 is reached in the peripheral area.