Estimates of humpback whale abundance off Kauai, 1989 to 1993:evaluating biases associated with sampling the Hawaiian Islands breeding assemblage

Abstract

Identification photographs of humpback whales Megaptera novaeangljae, collected off Kauai during the years 1989 to 1993, were used to estimate population abundance off the Hawaiian Islands, USA A total of 790 different individuals (988 different observations) were identified during the study. Several mark-recapture procedures were applied to the data using closed population models (Chapman's modified Petersen, weighted mean of the Petersen. Darroch's maximum likelihood estimator [MLE], and Chao's M,, M,, and M,,, estimators) and an open population model (Fisher-Ford estimator). The majority of population estimates were between 2000 and SO00 animals, with broad and overlapping 95% confidence intervals. Inconsistencies in pair-wise Petersen estimates and poor fit to the Fisher-Ford model indicated that the populat~on of ind~v~duals was not identical for each sampling occasion. As a pnmary example of this, it is suggested that individuals captured in 1992 had a lower probability of capture in other years examined. Possibly the greatest problems In estimating abundance of this population dealt with temporary emigration and non-random mixing of the population between sampling occasions. After considering the range of estimates, and potential biases in the data set. I suggest that the abundance of humpback whales off the Hawaiian Islands is likely close to 4000 individuals, and most probably between 3000 and 5000. These estimates are considerably greater than those generated in the late 1970s and early 1980s and, if accurate, would indicate growth of the population over the past decade; however, it is strongly recommended that more representative and precise estimates be obtained for management purposes.

Geographic variation in killer whale attacks on humpback whales in the North Pacific: implications for predation pressure

“…Overall basin-wide estimates of the abundance of humpback whales in the North Pacific were estimated as 6010 (SE = 474) in the early 1990s and appeared to be increasing as they recovered from commercial whaling (Calambokidis et al 1997). Abundance estimates show an increasing trend of about 8% per year for the California-Oregon-Washington feeding aggregation (Calambokidis & Barlow 2004) and 10% per annum for the population that migrates between Hawaii and Alaska (Mizroch et al 2004, Cerchio 1998. We cannot dismiss completely, however, the potential for some effect of predation on the rate of increase; the observed proportion of humpback whale calves in the US West Coast feeding area is lower than other humpback whale populations, although this could be biased by the timing of observations .…”

Population size and structure of whale sharks Rhincodon typus at Ningaloo Reef, Western Australia

“…The Chao estimator is particularly useful when the probability of capture is small (as in this study). Readers are directed to the original literature for more detailed information because the estimators are complex numerical functions without simple open-form solutions (Cerchio 1998). Program CAPTURE provides goodness-of-fit tests for each model and a model-selection procedure to identify the most probable model(s) (Otis et al 1978).…”

“…Thus, by examining the different temporal series separately, a better inter- The assumption of demographic closure tests the null hypothesis that the capture probability of individual i (p i ) is invariant at each sampling occasion. The alternative hypothesis is that some individuals have p = 0 at the beginning or end of the study period (Otis et al 1978, Cerchio 1998. Thus, the test is not sensitive to temporary emigration and can demonstrate low power when recaptures are low (Otis et al 1978).…”

Estimating survival and abundance in a bottlenose dolphin population taking into account transience and temporary emigration

“…Stevick et al 2003) or multi-sample estimators allow-ing for time variation, behavioural response and individual heterogeneity in capture probabilities (e.g. Cerchio 1998, Wilson et al 1999. Open-population models have also been used to estimate abundance (e.g.…”