Measuring the effects of a seasonal fishing closure on the abundance of Atlantic Cod (Gadus morhua) off the West Coast of Scotland Joanne Clarke 1*, David M Bailey 1, Peter J Wright 2 © Gilbert Van Ryckevorsel / WWF-Canada 1 University of Glasgow; 2 Marine Scotland Science * Catch control measures for commercial species are often at a spatial scale greater than that of local population dynamics, making individual spawning components vulnerable to extirpation Spawning aggregations often occur at times and places that are predictable making them more vulnerable to high levels of exploitation at this time Aggregative behaviour causes localised increases in catchability compared to other times of the year, resulting in high fishing mortality Therefore the introduction of an area closure during an aggregation period can reduce fishing mortality directly, whilst permitting sustainable exploitation outside of the spawning period Cod off the West Coast of Scotland are managed as a single stock within ICES Area VIa 3 sub-populations of cod have been identified within this area (Wright et al., 2006) Spawning stock biomass of cod off the West Coast of Scotland crashed during the late 90s A seasonal area closure was introduced to the mouth of the Clyde in 2001 to protect spawning cod Introduction 1 2 3

Objectives 1.Examine monthly Landings per Unit Effort (LPUE) 2.Compare annual trends in Catch per Unit Effort (CPUE) 3. Compare the length frequency distributions Methods Commercial landings per unit effort were investigated for each area prior to the area closure Clyde Trawls used were from within 60km distance of the known spawning aggregations of each of the 3 sub-populations The seasonal area closure was introduced into the mouth of the Clyde in 2001 prohibiting certain types of fishing during the spawning period Minch South West A Before/After, Control/Impact analysis was conducted to identify if there had been a change in trend of mature cod in the Clyde sub-population after the area closure was introduced compared to the other 2 sub-populations Aims To identify if cod aggregate in survey areas and determine if there has been an effect of the area closure on the sub- population of cod in the Clyde. Study Area BACI – B efore = A fter = C ontrol = Minch and SW I mpact = Clyde CPUE was grouped into 5 cm length bins to compare the length frequency distribution between “Before” and “After” for each sub-population. Catch per Unit Effort (CPUE) of mature cod caught by the international bottom trawl survey (IBTS) during quarter 1 were used for the analysis from 1986 to 2010.

Results BACI-Catch per Unit Effort (CPUE) Before After Commercial Data Sum of Landings Landings per Unit Effort Left Figure: Sum of total landings in Kilograms for each location for each month during time period for all vessel types. Right Figure: Mean (+/- SE) Corrected Landings Per Unit Effort (CLPUE) for vessels using Beam Trawl; Gill Nets Pelagic; Light Trawl; Trawl Single Demersal; Pair Trawl Demersal; Seine net and Nephrops trawl for each month for the time period Conclusion: Landings and catch rate (LPUE) peak for each area during the spawning period indicating aggregating cod The log of the fitted values ±1.96*standard error taken from the model of best fit for Catch per unit Effort (CPUE) for each sub-population “Before” (left) and “After” (right) the area closure. Conclusion: Model of best fit does not include 3-way interaction indicating no effect of the area closure on changes in population trends in the Clyde sub-population 1.Evidence of aggregations from elevated landings per unit effort (LPUE) 2.No evidence of a local recovery on the Clyde sub-population from trends in Catch per Unit Effort (CPUE) 3.No evidence of changes in length frequency distributions after the area closure in the Clyde sub-population, but no larger size class of cod being caught Why no recovery of cod in the Clyde? too little too late? Length Frequency Distribution using Kolmogorov-Smirnoff (K-S) test Clyde K-S test, D=0.25, p =0.16 Before After Conclusion: No significant difference in length frequency distributions between “Before” and “After” area closure for each of the sub-populations, but reduction in larger size classes being caught in the “After” period Conclusions