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Summary of the West Coast Rock Lobster Managed Fishery science and modelling review

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A full list of Fisheries Research Reports is available online at www.fish.wa.gov.au. The Chief Executive Officer of the Department of Primary Industries and Regional Development and the State of Western Australia accept no liability whatsoever, whether negligent or otherwise, arising from the use or release of this information or any part thereof. An independent peer review of the science and modeling related to the West Coast Lobster Managed Fishery was undertaken in May/June 2018.

The review was conducted as two separate components: a scientific review attended by an international reviewer, industry stakeholders and scientists from the Department of Primary Industries and Regional Development (DPIRD), and a modeling review attended by the same attendees as the scientific review with the addition of two more international reviewers. There were a number of unresolved issues, both from DPIRD and from industry, that emerged in the scientific review which then became the terms of reference for the subsequent modeling review. In addition, the evaluators made a number of recommendations that they felt would add value to fisheries management and further improve the stock assessment process.

Introduction

Science Review

Outcomes of Science Review / Terms of Reference

Are three models for assessing fisheries necessary or should they be reduced/changed (is there a more efficient process). What is seen during fishing does not reflect the growth of biomass in the models. Has spatial variation in recruitment been accurately captured in the model and has it changed over time.

Modelling Review

Outcomes of the Modelling Review - Recommendations

For the Biomass Dynamics Model (BDM), provide explicit and documented comparison of the implied stock dynamics with those from the integrated model over the same periods and explore the inclusion of some spatial dynamics. Attempt to obtain data from coastal areas through either expansion of the Independent Breeding Stock Survey (IBSS) or the masked pot sampling program. Examine alternative CPUE scenarios against time series data and changes in catchability.

Maintain puerulus sampling at current levels and possibly expand to include areas considered to have lower productivity levels. Continue to improve the documentation of CPUE standardization and consider alternative CPUE scenarios according to TOR 4. Extend either fishery-dependent or independent masked seine sampling to areas considered to exhibit lower productivity levels.

Actions arising from the review process

This document will continue to be produced and will be included as an appendix in the quinquennial updates of the Resource Assessment Report for the Western Rock Lobster Resource. The new simplified version of the IM will be developed on a more contemporary platform (TMB). 2.3-For the Biomass Dynamics Model, provide an explicit and documented comparison of the implicit stock dynamics with those of the Integrated Model over the same periods and explore the inclusion of some spatial dynamics.

DPIRD plans to maintain all three models and add an additional simplified version of the current IM by 2020. 4.1-Effort to obtain data from coastal areas through either expansion of the IBSS or the meshpot sampling program. The processes outlined in this document will be applied to WRL data and reported on in the subsequent publication of the Resource Assessment Report for this fishery.

Report from Science review

Data sources collected and used in the assessment of the fishery - Atypical sightings reported by fishermen. Catch rates may be affected by a reduction in the fleet, but they do not double solely as a result of halving the fleet. During the industry forum, concerns were again raised regarding the significant increase in biomass in the model from 2007 to 2010.

The industry's lack of confidence in the model outputs has led them to question the quality of the input data. DPIRD replied that it is accounted for in the model as it has a high spatial and temporal complexity (11 areas and 11 time steps each year). Based on both the model outputs and the sheer number of tags released (approximately 60,000 over the past three years), the Department was satisfied with the amount of tag data used in the model.

Individual sites are used in modeling and will be shown in the workshop. This is what we use in the model and will be shown in the workshop. How the now accepted dead areas are reflected in the model used to calculate lobster biomass in the fishery.

Has data been collected from other areas of the plain to determine if other areas are now affected in the plain. The model considers the summer fishery at the Abrolhos where large amounts of the total island catch are taken over the edge in the deep water. Does the department have data on the number of pots used in the fishery and the number of days fished to catch the quota in each area.

How has the model been able to estimate much lower effort in most of the midfield, especially in the summer of the "white season". This mortality rate applies to high-grade lobsters and is therefore accounted for in the model. Low catch rates in shallow water areas at the heart of the fishery Presenter: Dr Tim Langlois.

TORs supplied to reviewers

It should be noted that the Big Bank, which is part of the northern deep sea area, was not as heavily exploited as the rest of the fishery until the 1990s. As such, its threshold value was set at the average of breeding stock levels in the early 1990s in this region (1993–1995 average). We propose that threshold reference levels be set at egg production levels when the fishery is fished at the equilibrium MSY level (or part thereof, e.g. 0.9MSY).

Currently, the Integrated Model (IM) is the only model officially used for WCRLMF stock assessment. The development of three models, all providing the WCRLMF level of assessment, provides an opportunity to compare their various strengths and limitations. Depending on the construction of the new HSDR, this model may not require such a fine spatial or temporal scale.

In addition, it is the only model of the three to include variable productivity due to population size, a relationship that may have begun to affect fisheries due to recent population growth. Rather, the outputs of this model are a very good cross-check with those of the IM or BDM, as it uses a very different data source and assumptions. What can be seen during fishing does not reflect the growth of biomass in the models.

Some fishermen believe that the IM and DBM estimates of the increase in legal lobster biomass (and therefore what the re-tagging model predicts the current biomass is) are too optimistic and do not reflect what they see in their catch. Some fishermen in the industry believe that the shallow water at the center of the fishery (Cliff Head) has decreased in its productivity and that this is not taken into account in the assessment. The relatively large Kalbarri Shallow Water area typically contributes about 3% of the total annual commercial catch, while the Cliff Head area contributes even less than that.

A reassessment of data critical to the WCRLMF assessment is required.

Agenda for Modelling review

Reviewers report

Both the period of change in the fishery and spatial details require special attention in future developments and possible revisions of the assessment modeling frameworks. Attempt to obtain data from coastal areas through expansion of the IBSS or meshed pot sampling program. If there is a continued decline in the northern fishery, this fixed distribution by area could exacerbate such dynamics.

To ensure that the model does not become overdeveloped, strategies should be adopted to simplify the description of the inventory dynamics of the integrated model and to compare the simplified versions with the current version. The implementation of the mark-recapture study and the resulting model were very well executed. A serious limitation of TRM is that the reporting rate of labels was very low, on the order of 12%.

Simplification will alleviate this problem and open up further options for the maintenance and management of the western stone crayfish. The IB predicts that the stock biomass will increase, but industry representatives have stated that this is not the case in certain areas, especially in the coastal areas in the north of the fishery. This view requires consideration given recent changes in the dynamics of the fishery as there has been a large reduction in effort due to the structural changes in the fishery.

Unfortunately, IBSS does not sample the water at the depths where industry members have noticed a sharp decline in the amount of lobsters to be caught. Due to the increased importance of IBSS, this time series must be maintained and possibly extended if possible. Unfortunately, none of the puerulus collection sites are located in the current 'dead zone', although there are two that are currently close to its borders.

Currently, the origin of the 'dead zone' and of reduced numbers and low recruitment in this area is unknown. The consequences of the reported reduction in recruitment between Jurien Bay and 7 Mile Beach will not become apparent until the next few years. Certainly more research needs to be done on the recruitment implications of recent changes using the models.

Figure 1. Copied from the presentation made by Dr de Lestang at the WRL Modelling Review     on 31 st  May, 2018
Figure 1. Copied from the presentation made by Dr de Lestang at the WRL Modelling Review on 31 st May, 2018

Figure

Figure 1. Copied from the presentation made by Dr de Lestang at the WRL Modelling Review     on 31 st  May, 2018
Figure 2. A plot of the puerulus counts from 1970 – 2013 above the total reported catches for     the years 1974 – 2017 (a lag of four years
Figure 3. The series of puerulus counts (approximate analysis only; updated draft data using     Warnbro, Lancelin and Jurien only, provided by Dr de Lestang) from 1969 – 2017
Figure 5.  The mean puerulus count per collector (copied directly from the DPIRD presentation  to  the  reviewers)
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