De las troneras

According to the New Zealand threat classification system described by Molloy et al. (2002) and recently revised by Townsend et al. (2008), common dolphins are ‘Not threatened’ within New Zealand waters (Hitchmough et al., 2007). This designation was reached by consensus of a marine mammal expert panel which convened in 2001 and 2004 (Hitchmough, pers. comm.). Interestingly, the composition of both expert panels revealed most participants were either pinniped researchers or scientific experts more familiar with inshore threatened species. Disappointingly, neither panel included the caretaker of the national strandings database or any personnel associated with the systematic necropsy and reporting of pathology in New Zealand marine mammals. This

is surprising given that mortality data would appear imperative for detecting potential declines within a population. Indeed, the grounds on which this classification was derived appear somewhat ambiguous. According to Hitchmough (2002), the process for evaluating each taxon involves the distribution of questionnaires to “experts within and beyond the New Zealand Department of Conservation”. Hitchmough (2002) states, an expert panel would then discuss each taxon “for which information was available in the form of a completed questionnaire, a recent publication on status, or unpublished information known to panel members”. On the basis of the threat classification criteria (Molloy et al., 2002; Townsend et al., 2008), species resident within New Zealand waters are subject to ‘evaluation’ prior to classification as either ‘Extinct’ ‘Threatened’ or ‘Not threatened’ (Figure 8.1). However, based on the lack of any formal ‘evaluation’ being conducted on common dolphins, ‘evaluation’ in this instance appears to relate to that outlined in Hitchmough (2002), namely “unpublished information known to panel members was assessed by panel members according to the Molloy et al., (2002) criteria”.

Members of both 2001 and 2004 expert panels acknowledged a lack of species-specific data for common dolphins (Hitchmough, pers. comm.). Nonetheless, a classification of ‘Not threatened’ was still deemed to be the most appropriate classification for this species. In the absence of scientific data, it would appear that the classification of the New Zealand common dolphin was based solely upon anecdotal information relating to “frequent sightings of this species at certain locations around New Zealand” (Hitchmough pers. comm.) Of course, frequent sightings of a species in disjunct ‘hotspot’ locations do not necessary constitute stability, as has recently been demonstrated in the declining Mediterranean Sea common dolphin population (Bearzi et al., 2008). Further concerns arise when a species is classified as ‘Not threatened’ on the basis that “….there was no evidence produced of a decline at a level sufficient to trigger listing in any of the threatened categories” (Hitchmough, pers. comm.). Exactly on what grounds a decline could be detected, should it have occurred, appears unclear especially since no baseline data regarding abundance, life history or mortality levels are available or were presented during either of the previous classification expert panel meetings.

Figure 8.1 The New Zealand threat classification system (Source: Molloy et al. 2002).

Recently, revisions have been made to the New Zealand threat classification system (Townsend et al., 2008). Of particular consequence to Delphinus is the qualifier that taxa ‘not assessed’ are considered ‘Data deficient’ (Figure 8.2). However, as highlighted previously, the term ‘assessed’ appears to be somewhat ambiguous in that it would appear anecdotal observations alone warrant ‘assessment’. Within the updated classification system, Townsend et al. (2008) define ‘Not threatened’ as taxa that are assessed and do not fit any of the other categories. Where information is so lacking that an assessment is not possible, taxa are assigned to the ‘Data deficient’ category. Townsend et al. (2008) state that if taxa are listed in a category other than ‘Data deficient’ but confidence in the listing is low due to poor-quality data, then the listing can be qualified with the letters ‘DP’ (Data poor). However, in the case of Delphinus this does not resolve the issue since the absence of key demographic data (abundance/density estimates, calving intervals) as opposed to ‘quality of data’ still remains the issue. Classifying any species as ‘Not threatened’ without such data is arguably erroneous on the basis of there being no science on which to corroborate such an assumption. Townsend et al. (2008) confirm that “Collection of sufficient demographic data to allow evaluation is a high priority for ‘Data deficient’ taxa”.

Currently, fourteen marine mammal species are classified as ‘Data deficient’ within New Zealand waters, including the pygmy sperm whale (Kogia breviceps) and various species of beaked whale (Mesoplodon spp.) (Hitchmough et al, 2007). As with the common dolphin, all of these species lack abundance and density estimates.

Furthermore, similar to Delphinus, most lack baseline data describing their reproductive biology, diet and general life history. Notably, however, some have taxonomic, diet and/or life history diet available within the published literature (Dalebout et al., 1998; Dalebout et al., 2004; Dalebout et al., 2005; Plön & Bernard, 2006). Indeed, data required for successful management (i.e. taxonomy, life history) are more readily available within the literature for some of these listed species than for common dolphins. This fact, alongside the numerous human-induced impacts faced by this species, exemplifies why Delphinus should be reclassified as ‘Data deficient’ within New Zealand waters.

Figure 8.2 The revised New Zealand threat classification system (Source: Townsend et

al., 2008).

8.3.2 Management

As part of the management of New Zealand’s marine mammals, the Department of Conservation has issued a Marine Mammal Action Plan covering the period 2005 to 2010 (Suisted & Neale, 2004). Focusing on resident species, the plan contains species- specific actions plans for all but one of New Zealand’s resident marine mammal species. Despite being subject to a range of anthropogenic impacts, common dolphins are the

only resident cetacean in New Zealand waters to lack a species-specific action plan (Suisted & Neale, 2004). Erroneously, common dolphin feature under section ‘2.16 Other toothed cetaceans’, an extended appendix alongside vagrant species such as rough-toothed dolphin (Steno bredabensis), spectacled porpoise (Phocoena dioptrica), Risso’s dolphin (Grampus griseus), hourglass dolphin (Lagenorhynchus cruciger) and striped dolphin (Stenella coeruleoalba). The presence of these vagrant species within New Zealand waters, is by definition, rare. Furthermore, such species are not the target of a commercial tourism industry, are not identified as by-catch within New Zealand fisheries, and do not appear at risk from pollutants evident within New Zealand waters. Nonetheless, Suisted & Neale (2004) stated “…there are generally few known conservation or management issues” when referring to common dolphins. Clearly, current data reveal this not to be the case and thus, the inclusion of common dolphins within a ‘vagrant’ appendix is nonsensical.

Managing marine mammal populations is problematic, especially when dealing with a species for which there is limited biological information available. In the United States, National Marine and Fisheries Services (NMFS) use the term ‘stock’ to describe management units. Generally, stock identification uses the best biological information available to describe biological differences and stock structure (Dizon, 2002). However, as highlighted throughout this thesis, there is a complete lack of empirical data relating to the biology and life history of common dolphins within New Zealand waters. Such constraints hamper our knowledge of identity, ‘stock’ and ‘population’ definitions within New Zealand waters. The status quo is the neglect of Delphinus by the management agency responsible for marine mammal conservation in New Zealand. This has resulted from the use of untested assumptions, and is in spite of several proven anthropogenic impacts.