Separating the effects of climate, bycatch, predation and harvesting on tītī (Ardenna grisea) population dynamics in New Zealand: A model-based assessment

Abstract

A suite of factors may have contributed to declines in the tītī (sooty shearwater; Ardenna grisea) population in the New Zealand region since at least the 1960s. Recent estimation of the magnitude of most sources of non-natural mortality has presented the opportunity to quantitatively assess the relative importance of these factors. We fit a range of population dynamics models to a time-series of relative abundance data from 1976 until 2005, with the various sources of mortality being modelled at the appropriate part of the life-cycle. We present estimates of effects obtained from the best-fitting model and using model averaging. The best-fitting models explained much of the variation in the abundance index when survival and fecundity were linked to the Southern Oscillation Index, with strong decreases in adult survival, juvenile survival and fecundity being related to El Niño-Southern Oscillation (ENSO) events. Predation by introduced animals, harvesting by humans, and bycatch in fisheries also appear to have contributed to the population decline. It is envisioned that the best-fitting models will form the basis for quantitative assessments of competing management strategies. Our analysis suggests that sustainability of the New Zealand tītī population will be most influenced by climate, in particular by how climate change will affect the frequency and intensity of ENSO events in the future. Removal of the effects of both depredation by introduced predators and harvesting by humans is likely to have fewer benefits for the population than alleviating climate effects.

Climatic Effects on Grey-Faced Petrel (Pterodroma gouldi) Chick Growth and Survival

“…The effects of annual variations in climate in addition to predators can thus be the difference between positive and negative growth for a colony. This has also been demonstrated on southern islands of New Zealand where the Sooty Shearwater (Ardenna grisea) breeds, although for this species the climatic effect is opposite in direction with improved breeding success in La Niña years [33,34]. The Grey-faced Petrel colony on Te Hāwere-a-Maki has remained constant in size around approximately 100 burrows for at least two decades (JCR unpubl.…”

Broad‐scale climate variation drives the dynamics of animal populations: a global multi‐taxa analysis

“…Thirty‐eight bird species showed a significant association with ENSO − (Table 1), including studies from Canada, the USA, Mexico, Jamaica, Costa Rica, Panama, Ecuador, Peru, Brazil, South Georgia, the UK, Spain, Seychelles, French Sub‐Antarctic Islands, Australia, New Zealand, and Antarctica (Chastel, Weimerskirch & Jouventin, 1993; Lyver, Moller & Thompson, 1999; Sillett, Holmes & Sherry, 2000; Gaston & Smith, 2001; Ramos et al ., 2002; Barbraud & Weimerskirch, 2003; Jenouvrier et al ., 2005; Mazerolle et al ., 2005; Chambers & Loyn, 2006; Forcada et al ., 2006; Sedinger et al ., 2006; Vargas et al ., 2006, 2007; Lee, Nur & Sydeman, 2007; Balbontin et al ., 2009; Devney, Short & Congdon, 2009; Norman & Chambers, 2010; Rolland et al ., 2010; Wolf et al ., 2010; Ancona et al ., 2011; Baylis et al ., 2012; Schmidt et al ., 2014; Woehler et al ., 2014; Wolfe, Ralph & Elizondo, 2015; Horswill et al ., 2016; Townsend et al ., 2016; Anderson et al ., 2017; Sandvig et al ., 2017; Barbraud et al ., 2018; Velarde & Ezcurra, 2018; Woodworth et al ., 2018; Jones & DuVal, 2019; McKechnie et al ., 2020; Tavares et al ., 2020; Cleeland et al ., 2021; Smart, Smith & Riehl, 2021). These 38 bird species spanned a broad range of taxa, with seabirds (penguins, petrels, albatrosses, auks, gulls) and New World warblers well represented.…”

The impact of ocean warming on selected commercial fisheries in New Zealand

“…The latter is in line with the observation that climate change‐induced warming promotes the growth of nearshore snapper and tarakihi (Morrongiello et al., 2021). Aquaculture species such as salmon and mussels (Broekhuizen et al., 2021) and marine birds (McKechnie et al., 2020) are also affected by ocean warming. A shift in the distribution range in response to warming has been reported for different marine species (Poloczanska et al., 2013), and so the projected increase in SST may result in increasing dominance of warmer‐water species in NZ waters.…”