Abstract
The United Nations General Assembly has called for the adoption of conservation management measures to protect vulnerable marine ecosystems (VMEs) from significant adverse impacts outside of areas of national jurisdiction. In response, many regional fisheries management organisations (RFMOs) have implemented move-on rules triggered by encounter threshold levels for the biomass of VME indicator taxa retained as bycatch. However, due to uncertainty of the relationships between catch, catch efficiency and the in-situ biomass of VME indicator taxa, move-on rules alone may not be enough to prevent significant adverse impacts on VMEs. Although spatial management measures present one possible solution to these concerns, a lack of empirical data on the distribution of VMEs within the high seas means spatial management is often informed by model predictions of the spatial distribution of VME indicator taxa. Given the uncertainty associated with predicted distributions, move-on rules can provide immediate responses when spatial management measures may not be providing the expected conservation benefits. Using bycatch data from 9,771 New Zealand bottom trawls within the South Pacific RFMO Convention Area, we illustrate a data-informed approach for selecting high move-on encounter thresholds that may suggest the predicted distributions of VME taxa used to underpin spatial management are highly inaccurate. The reasoning that high thresholds act as a safeguard against uncertainty in the performance of spatial management measures requires untested assumptions regarding the level of permissible bycatch before further management action is required, with the acceptance of those assumptions a management decision balancing the sensitivity of the move-on rule with uncertainty regarding the effectives of the spatial management measures. Additional work is required to support these management decisions, including the determination of taxa-specific catchability estimates, and the seafloor density/biomass of VME indicator taxa that represents a VME. Obtaining this information will allow for the identification of encounter thresholds that are more ecologically meaningful. In the interim, the choice of thresholds should be re-evaluated as more experience with their application is gathered.
Highlights
Based on growing concern about the risks to vulnerable marine ecosystems from fishing activities, the 2005 United Nations General Assembly (UNGA) has called for application of a precautionary approach and ecosystem approaches in the identification of vulnerable marine ecosystems, assessments of whether individual bottom fishing activities would cause significant adverse impacts to those ecosystems, and the closure of areas where vulnerable marine ecosystems are known or likely to occur until conservation and management measures have been established to prevent significant adverse impacts (United Nations General Assembly [UNGA], 2005, 2007)
The prevalence of each of the ten vulnerable marine ecosystems (VMEs) indicator taxa in the 9,771 bottom trawl tows conducted by New Zealand in the SPRFMO Convention Area between 2008 and 2018 was highly variable, ranging from two observations (
The spatial management measures currently used by SPRFMO (SPRFMO CMM 03-2019) are based on habitat suitability models (Georgian et al, 2019) and only areas containing no or few cells with high conservation value for VME indictor taxa are open to bottom trawling (Delegation of New Zealand, 2019)
Summary
Based on growing concern about the risks to vulnerable marine ecosystems from fishing activities, the 2005 United Nations General Assembly (UNGA) has called for application of a precautionary approach and ecosystem approaches in the identification of vulnerable marine ecosystems, assessments of whether individual bottom fishing activities would cause significant adverse impacts to those ecosystems, and the closure of areas where vulnerable marine ecosystems are known or likely to occur until conservation and management measures have been established to prevent significant adverse impacts (United Nations General Assembly [UNGA], 2005, 2007). The guidelines have served as the principle means for RFMOs to define and manage significant adverse impacts on VMEs, they do not provide any clear guidance on what constitutes evidence of an encounter with a VME during bottom fishing operations or analytical approaches for identifying whether an area contains a VME or not. Recognizing a lack of specificity in the guidelines, and that the actions that they had called for had not been sufficiently implemented by all RFMOs, the UNGA has become increasingly explicit regarding the need to develop science-based protocols to define evidence of encounters with VMEs, including the implementation of indicator-specific encounter thresholds, which in turn trigger a response, such as ceasing fishing operations and relocating elsewhere (i.e., the ‘move-on rule’) (United Nations General Assembly [UNGA], 2010, 2012). An ongoing challenge for RFMOs and member states is how to determine, based on best available scientific information and the precautionary principle, suitable encounter threshold levels that take into consideration other management measures (e.g., effort controls, spatial restrictions or closures, changes in gear design and/or operational measures) that are in place to prevent significant adverse impacts on VMEs
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