On behalf of my co-authors, I am pleased to announce our recent publication in Marine Mammal Science:
Wickman, L., Rayment, W., Slooten, E., & Dawson, S. M. (2021). An observed decline in the mark rate of Hector's dolphins at Banks Peninsula, New Zealand. *Marine Mammal Science*, 1– 8. *https://doi.org/10.1111/mms.12826 <https://doi.org/10.1111/mms.12826>* SUMMARY Capture-recapture analyses on marine mammals typically assume mark rate (the proportion of individuals with unique, recognisable natural marks) is constant over time. This assumption may not be true if changes in management have decreased the frequency of interactions with fishing gear (a known source of marks). We hypothesized that mark rate in the Banks Peninsula population of Hector’s dolphins has declined since the establishment of area-based protection from gillnetting. After filtering by image quality, our analysis used 2,363 images of 160 groups of dolphins obtained from 1992 – 1996, and 1,133 images of 163 groups obtained in 2016. These images were categorised by mark quality, with individuals having very obvious marks (Cat 1 & 2) retained to estimate mark rate. Mark rate was estimated for each time period using a hierarchical Bayesian model. The Bayesian model estimated the mean mark rate of the population as 0.107 (95% HDI: 0.080 - 0.137) for the period of 1992–1996, and 0.069 (95% HDI: 0.049-0.090) in 2016, indicating a 98% probability that the mark rate in 2016 was lower than the 1992 –1996 period. The lower mark rate in 2016, along with previous evidence of improved survival rate after area-based protection, may suggest encounters between dolphins and fishing gear have declined. The note may be obtained at https://onlinelibrary.wiley.com/doi/10.1111/mms.12826, or you may email me at lindsaymwick...@gmail.com for a .pdf copy. If you’d like to know more about the methods used to estimate mark rate in this paper, I’d like to refer you to our recent, previous publication: Wickman, L., Rayment, W., Slooten, E., Dawson, S.M. (2021). Recommendations for estimating mark rate of cetaceans in photo-ID research: A critique of field sampling protocols and variance estimation. *Marine Mammal Science,* 37: 328–343. https://doi.org/10.1111/mms.12723 Cheers, Lindsay Wickman
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