Distribution, abundance and biology of Group V humpback whales ...

More documents

Recommendations

Info

Variations in the abundance of prey on feeding grounds may be directly related to the year-to-year variation in reproductive rates (Clapham 1996) and abundance on the wintering grounds (Chaloupka and Osmond 1999). Wiley and Clapham (1993) tested the hypothesis of whether or not maternal condition affects the sex ratio of offspring. Their investigation concluded that the sex ratio of calves born to females in “superior” condition, or that had a calving interval of three years, was biased toward sons. 7.4 Male reproduction and behaviour Mature male humpback whales depart the feeding grounds with mature females (Dawbin 1966). Humpback whale courting behaviour includes elaborate songs sung by males during their migration to (Charif et al.2001) and on wintering grounds (Helweg et al.1998b). Helweg and Herman (1994) found there was no difference between singing behaviour during day and night in deep water, although Au et al.(2000) found that in shallow water off Maui there was a change in the occurrence of singing behaviour with time of day, with a peak at night. The song patterns produced by singing humpback whales depend on where individuals live, with populations inhabiting different ocean basins normally singing quite distinct songs (Noad et al.2000). Singing whales have been used to determine migratory routes (Charif et al.2001), demonstrate interchange between populations (Helweg et al.1998) and as an index of abundance (Noad 1998). Mobley et al.(1988) played a variety of sounds to humpback whales on wintering grounds and concluded that the different rates of behavioural response were attributed to the behaviour of sexually active males seeking to affi liate with sexually mature females. A study conducted by Frankel et al.(1995) supported the hypothesis that song functions to maintain distance between singers and McCauley et al.(1995) give a succinct description of the song and hearing capabilities of humpbacks. Richardson et al.(1995) is a comprehensive review of acoustics and how they relate to marine mammals. The information presented includes specifi c references to humpback whales. They concluded there is no research to demonstrate that acoustics adversely affects humpback whales. However, more recent research demonstrates that humpbacks alter their behaviour in response to anthropogenic noise (Miller et al.2000). Williams et al.(2002) concluded that weakening or not enforcing the minimum approach distances for the whale watching of orcas in Canada would result in higher levels of disturbance. Corkeron (1995) demonstrated that humpbacks in Hervey Bay altered their behaviour when vessels were within 300m. This and several other studies show that the behaviour of humpbacks is altered by the presence of vessels but it remains uncertain if the effect is detrimental (Bauer and Herman 1986; Baker and Herman 1989; Bryden et al.1988). 8 Population estimates and rates of increase Reviews of international data indicate a strong recovery in most studied humpback whale populations (Best 1993 and Clapham 1999b). Paterson et al.(1994) suggests that the level of recovery of the Group V population, in the post-whaling period, is due to the stock experiencing no detrimental environmental factors. 8.1 Southern hemisphere population estimates During 1933–1939, the estimated total number of southern hemisphere baleen numbered 220,000–340,000. Approximately 10 percent of the southern hemisphere stock of baleen whales was humpback whales, and the ratio between the groups I–V was considered to be 1:1:2:3:3 respectively (Matthews 1957 cited Chittleborough 1965). Based on these estimates the Group V population could be estimated at 22,000–34,000 individuals for 1933–1939 (Figure 8). 8.2 Group V population estimates Figure 8 is a summary of the population estimates and illegal catches by the Soviet fl eet for Group V humpbacks during 1930–2005. Chittleborough (1965) estimates the Group V pre-whaling population numbered approximately 10,000 individuals. By 1960, he estimated a population size of only 500 individuals. In 1963, the International Whaling Commission (IWC) imposed a ban on whaling, and in 1964 the Group V population was estimated at just 400 individuals. Until 1963, humpback population estimates were derived by modelling the fi sheries-based catch per unit effort data (Chittleborough 1965). Chittleborough (1965) compared population estimates derived by two methods and argues that for the estimate to be correct using the DeLury method, a further 5000 humpbacks would have had to been fi shed during the years 1960 and 1961. Only 302 and 270 whales were reported to the IWC for each of those years. Although there is some uncertainty in these estimates, it is clear that during the late 1950s and early 1960s, the Group V population experienced a signifi cant decline in numbers. Recent data presented by Mikhalev (2000) supports DeLury’s population estimate discussed by Chittleborough (1965). Mikhalev (2000) presented data collected by two Soviet vessels illegally whaling during the summer season of 1959 in the Antarctic Area V. The Russian vessels signifi cantly exceeded the quota for all countries by illegally fi shing a total of 11,605 individuals from the Group V population. Chittleborough (1965) estimated that the Group V population would take 36–63 years to regain its unfi shed status of 10,000 individuals. However in 1998, 33 years later, the Group V population was estimated at 4000 individuals (Paterson cited QDEH 1999). If a constant rate of increase is assumed, the 1962 population estimate of 500 individuals would have to have increased at a rate of approximately 8 percent a year to reach its unfi shed state in 36 years. The rate of increase for the population to reach its unfi shed state in 63 years is just 4·8 percent a year. However, Mikhalev (2000) details the large-scale illegal Soviet catch data for the late 1960s and illustrates that the catches of humpback on their feeding grounds during 1963–1968 exceeds the population estimates derived by Chittleborough (1965). The population estimates for this period are being revised to account for the illegal catches by the Soviet fl eet (pers. comm. P Corkeron 2002). 14 • Distribution, abundance and biology of Group V humpback whales Megaptera novaeangliae: A review • August 2002
8.3 Group V rates of increase In Queensland, three independent groups, using data collected by two different methods, have modelled the rate of increase of the population. Paterson et al.(1994) and Bryden et al.(1997) conducted land-based surveys from Point Lookout, North Stradbroke Island, since 1978 and 1980 respectively. Paterson (1984), Paterson and Paterson (1989) and Paterson et al.(1994) estimate the population is increasing at 11·7 percent a year. Biennial surveys (1994–1996–1998) undertaken by the Patersons since 1992 confi rm an annual rate of increase of 11·6 percent (95 CI: ±1 percent). Both sets of shore-based data assume that whales travel at the same speed throughout the day and night (Paterson 1994). Chaloupka and Osmond (1999) modelled data collected as a secondary consideration by an enforcement agency undertaking an aerial surveillance program in the Great Barrier Reef Marine Park. They estimated a much lower rate of population increase of 3·9 percent a year. ? 34,000 in 1930: Matthews 1942 10,396 in tropical waters 1947-61: Dawbin 1997 10,000: Chittleborough 1965 Modern studies data: Bryden et al 1990, 1997; Patterson et al 1989, 1994; Patterson 1998 (cited QPWS 1998) 4600: DeLury 1947 500: Chittleborough 1965 Figure 9. Extrapolated rate of increase for Group V humpback whales 1980–2000 Since the ban on commercial hunting was implemented, the combined impact of international, national and state conservation legislation has contributed to an approximately 40 percent recovery in the Group V humpback whale population. In addition there are no signs that the population is approaching asymptotic level in response to prey resources, habitat availability or other population limiting factors. There are no indications that the introduction of commercial whale watching in Queensland in 1989, as managed by QPWS (EPA 2001), has caused any change in the rate of recovery of this species (Figure 9). Global ban on commercial humpback whaling in 1963 11,605 whales fi shed in Antarctic waters: Mikhalev 2000 10,000: Chittleborough 1965 800: Chittleborough 1965 Modern studies data Figure 8. Summary of estimated population size, numbers fi shed and associated references for the Group V population 1930–2000 15 • Distribution, abundance and biology of Group V humpback whales Megaptera novaeangliae: A review • August 2002
Page 1 and 2: Distribution, abundance and biology
Page 3 and 4: Contents 1 Introduction............
Page 5: Figure 1. Queensland marine parks a
Page 8 and 9: Figure 4. Group IV and V distributi
Page 10 and 11: The main calving ground of the east
Page 12 and 13: During the northern migration there
Page 14 and 15: 6.1.2 Sloughed skin sampling Slough
Page 18 and 19: Appendix 1. Summary of population e
Page 20 and 21: Craig, A.S. & Herman, L.M. 1997. Se
Page 22: 20 • Distribution, abundance and

Distribution, abundance and biology of Group V humpback whales ...

You also want an ePaper? Increase the reach of your titles

Delete template?

Save as template?