Shark tagging: Equipment and training for the estimation of post-release mortality of sharks. NIWA Client Report 2017413WN

The purpose of fisheries management is to ensure that populations can be exploited in a sustainable
manner. This requires accurate information on mortality due to fishing. Mortality due to fishing
activities has long been synonymous with catch but there is a growing recognition that catch
statistics, particularly those representing landed catch, may greatly under-represent the actual
number of fish removed from the current and future stock. This is especially true for fishes such as
sharks which may be discarded (whole or in part) or released in large numbers either because of
regulations or lack of market demand. In many cases, discarded or released sharks are often not
enumerated at all; if they are enumerated there is often no record of their condition; and even if
there is a record of their condition that condition may not be a reliable predictor of their survival. As
a result, there is considerable uncertainty about the number of sharks killed through fishing activities
and this uncertainty leads to a lack of clarity in defining and refining shark conservation and
management.
The Western and Central Pacific Fisheries Commission (WCPFC), along with the four other tuna
Regional Fisheries Management Organizations (t-RFMOs), is a partner in the Areas Beyond National
Jurisdiction (ABNJ) – often referred to as Common Oceans – Tuna Project. The objective of this
project is to achieve efficient and sustainable management of fisheries resources and biodiversity
conservation in marine areas that do not fall under the responsibility of any one country. One set of
activities of the GEF-funded ABNJ Tuna Project aims to reduce the impact of tuna fisheries on
biodiversity by improving data and assessment methods for sharks, thereby promoting their effective
management. Within this set of activities WCPFC has been tasked with conducting a major study of
shark post-release mortality (PRM) in its longline fisheries. The first stage in this process culminated
in a workshop on methods for estimating shark PRM. The workshop produced a survey design that
called for the deployment of 200 ‘survival’ popup electronic tags on 100 shortfin mako and 100 silky
sharks in selected areas of the Pacific Ocean.
For stage two of the project, the New Zealand surface longline tuna fishery was chosen for the
deployment of 33 tags by Ministry for Primary Industries (MPI) fisheries observers on shortfin mako
sharks caught as bycatch within the fishery. For stage three of the project, the Fiji surface longline
tuna fishery was chosen for the deployment of 83 survival tags by Fiji Fishing Industry Association
(FFIA) vessels and Ministry of Fisheries observers on 33 shortfin mako sharks and 50 silky sharks.
This report was prepared as a resource for training Fiji Fishing Industry Association officers and crew,
and Fiji Ministry of Fisheries Observers.