Historically, exploited marine mammal species, such as sea lions, fur seals, right whales and humpback whales, were severely depleted in abundance. Today, some species are slowly increasing in numbers, though this is not the case for all marine mammal populations throughout their ranges.

 

Sea lions are declining in abundance at the Auckland Islands, the most important of the remaining colonies. The reasons for this decline are not known, though major outbreaks of disease and fisheries bycatch may be implicated.

Although the status of fur seals is unknown, they appear to be increasing in numbers throughout much, but not all, of their range. Doubt exists for those found off the west coast of South Island, where there is some suggestion from the Department of Conservation (DoC) that their abundance is declining. DoC has suggested that this may be due to a number of causes, including climate-driven changes and fisheries bycatch.

Southern right whales and humpback whales appear to be slowly increasing in numbers in the absence of all harvest.

The single greatest cause of Hector’s and Maui’s dolphin human-caused mortalities is reported to be from fisheries related deaths. Hector’s and Maui’s dolphins are subject to incidental take in recreational and commercial set net and trawl fisheries. Human-caused threats to these dolphins have been included in a joint MFish and DoC Threat Management Plan, which resulted in fisheries restrictions being established throughout much of their range.