Capture-recapture abundance and survival estimates of three cetacean species in Icelandic coastal waters using trained scientist-volunteers

Abstract

Knowledge of abundance and survival of humpback whales, white-beaked dolphins and minke whales are essential to manage and conserve these species in Icelandic coastal shelf waters. Our main goal was to test the feasibility of employing inexpensive research methods (data collected by trained-scientist volunteers onboard opportunistic vessels) to assess abundance and apparent survival. No previous studies in Iceland have investigated these two demographic parameters in these three cetacean species using open capture-recapture models accounting for imperfect and possibly heterogeneous detection. A transient effect was accounted for whenever required to estimate the population of resident individuals. Identification photographs were collected by scientist-trained volunteers for 7years (2006–2013) from onboard commercial whale-watching vessels in the coastal waters of Faxaflói (southwest coast, ~4400km2) and Skjálfandi (northeast coast, ~1100km2), Iceland. We estimated an average abundance of 83 humpback whales (Mn; 95% confidence interval: 54–130) in Skjálfandi; 238 white-beaked dolphins (La; [163–321]) in Faxaflói; and 67 minke whales (Ba; [53–82]) in Faxaflói and 24 (14–31) in Skjálfandi. We also found that apparent survival was constant for all three species (Mn: 0.52 [0.41–0.63], La: 0.79 [0.64–0.88], Ba-Faxaflói: 0.80 [0.67–0.88], Ba-Skjálfandi: 0.96 [0.60–0.99]). Our results showed inter-annual variation in abundance estimates which were small for all species, and the presence of transience for minke whales. A significant increase in abundance during the study period was solely found in minke whale data from Skjálfandi. Humpback whales and white-beaked dolphins showed lower apparent survival rates compared to similar baleen whale and dolphin populations. Our results show data collected by trained-scientist volunteers can produce viable estimates of abundance and survival although bias in the methods we employed exist and need to be addressed. With the continued increase in anthropogenic pressures on our three target populations in Iceland our results can be used by relevant stakeholders to develop appropriate conservation strategies in the region.