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Influence of krill (Euphausia superba) availability on humpback whale (Megaptera novaeangliae) reproductive rate


Seyboth, Elisa; Félix, Fernando; Lea, Mary-Anne; Dalla Rosa, Luciano; Watters, George M.; Reid, Keith; Secchi, Eduardo R.




Marine Mammal Science










Body condition, euphausiid, humpback whale, krill, megaptera novaeangliae, platforms of opportunity, Prey, reproductive rates, whale watching


We weighted krill density values as data are overdispersed (i.e., its variance ishigher than its mean), so that using the mean in the analysis would probably lead to a misinterpretation of thecorrelation between variables being tested. Cross-correlation methods allow the identification of the time lag thatmaximizes the correlation between the explanatory and the response variables (Legendre & Legendre, 1998) andwas run in PAST software version 3.0 (Hammer et al., 2001). The result was later used in a regression model run inR software version 4.0.2 (R Core Team, 2020) to test the relationship between krill biomass and RBR weighted byeffort (number of trips of each year). We considered a 0.05 level of significance in the analysis.Relative birth rates of humpback whales were computed from data collected during 278 whale-watching trips(M = 39.7 ± 7.9 per year) (Table 1). A total of 127 calves (M = 18.1 ± 13.2 per year) and 1,637 noncalves (M = 233.8± 130.4 per year) were recorded, excluding resights. The RBR (M = 0.07 ± 0.03) was significantly correlated with krilldensity in the previous year (i.e., lagged by 1 year; r2= 0.9, p = .02; Figure 2). The relationship between RBR and krilldensity in the previous year balanced by the number of trips was also positive and significant (r2= 0.8, p = .02).This is the first time that the relationship between environmental conditions around the Antarctic Peninsula andcalf production by humpback whales from Breeding Stock G has been investigated.
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