Preparing for ecosystem-based fisheries management: A Namibian case study Nico E. Willemse International Symposium “Marine fisheries, ecosystems, and societies in West Africa: half a century of change.” Dakar, Senegal, June 2002.

Introduction: Namibian Fisheries Location: West coast of Southern Africa, bathed by the Benguela upwelling, which supports rich fishery resources; Fisheries heavily exploited prior to Independence in 1990; No effective management in place before 1990; >300 distant water fleets (DWFs) roamed offshore from 1960s to 1980s.

Data and Methods 1 Landings: not recorded continuously – there was no effective monitoring agency; Hence landing time series had to be reconstructed; this was done for ; Mean trophic level of landings were then estimated: –First, a TL estimate was obtained (mainly from FishBase ( for each species; –Then mean TL values we obtained by weighing species’ TL by their landings.

Data and Methods 2 P/Z ratio of landings was obtained by: –Identifying species as either piscivorous (P) or zooplanktivorous (Z); –Deriving annual P/Z ratio by weighing each species by its landings. Plot mean TL vs landings, and mean P/Z vs. landings over 50 year period; Interpret trends based on biology of species, and behaviour of the DWFs.

Results 1: Three developmental stages observed: 1. Undeveloped ( ): not much change in indicators; 2. Developing/ mature ( ): rapidly increasing indicators; 3. Senescent ( ): declining trends of indicators. Post Independence: Most stocks are depressed: shadow of past overfishing and unfavourable environmental conditions.

Results 2: Catch composition analysis: shift from hakes (TL=4.5) to horse mackerel (TL=3.5); Landings, mean TL and P/Z ratio of landings declined, suggesting ’fishing down marine food webs’; Backward-bending plot of mean TL vs. landings plot implies: 1.’Fishing down’ does not lead to catch increases; 2.Hence the bottom-up tranfer of biolgical is impared by ecosystem impact of fishing.

Trends 1: Total landings Undeveloped Developing/ mature Senescent

Trends 2: Mean TL Mean TL declined from 4.0 between to 3.7 between

Trends 3: Mean TL vs P/Z Ratio Similar trends observed with difference in amplitude. Short-term fluctucations in P/Z ratio – periodic Benguela Niño.

Trends 4: Mean TL vs. Landings

Ecosystem Impact 1 Impaired bottom-up production transfer. Sardine collapse: –Replacement by other small pelagics; –Plankton community change; –Reduced competition for phytoplankton; –Food availability changed, which affected the piscivores; –’wasp-waist’ control impaired.

Ecosystem Impact 2 Decline of hake: –increase in other pelagic predators; –Increase in adult horse mackerel – opportunistic feeder. 16% Decline in ecosystem biomass in 1990.

Fishery Resources s Cape hake, horse mackerel and sardine: –Increased after 1990; decreased thereafter; –Similar for most species caught off Namibia. Current state of stock: severely depressed, due mostly to the Benguela Niño event of 1994/5.

Fisheries Management s National issues: –Stock rebuilding policy; –90% reduction of DWFs; –Biological vs. political imperatives; –Benguela Niño impacts. Regional issues (Namibia, South Africa and Angola): –Management of shared and migratory stocks; –Improved research capacity; –Ecosystem modelling and transition to ecosystem- based management.

Preparing for ecosystem-based management: Reconstructed time series of landings for 50 years, i.e., a long period, to allow for contrasts; Interpreting the resulting trends in terms of fisheries impact on ecosystem, mediated by biological interactions, and environmental change, and thus: Considering more than one species, one fleet at a time; Which his should contribute to better management, and more long-term benefits gained from the resource.

Acknowledgements Thanks are due to my professors who helped me extensively in finishing my thesis in time: Prof. Jorge Santos of the University of Tromso and Prof. Daniel Pauly of the University of British Columbia; The Sea Around Us project, which funded my participation in this symposium, is a UBC Fisheries Centre partnership with the Pew Charitable Trusts of Philadelphia, USA.