AN ECOSYSTEM-BASED APPROACH TO STUDY TWO DOLPHIN POPULATIONS AROUND THE ISLAND OF KALAMOS, IONIAN SEA, GREECE by CHIARA PIRODDI B.Sc. Ca’ Foscari University of Venice, 2004 A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE in THE FACULTY OF GRADUATE STUDIES (Zoology) THE UNIVERSITY OF BRITISH COLUMBIA (Vancouver) February 2008 Chiara Piroddi, 2007 Abstract In the northeastern Ionian Sea, two populations of dolphins, the short- beaked common dolphin (Delphinus delphis) and the common bottlenose dolphin (Tursiops truncatus), have been studied since 1993 by the Tethys Research Institute, Italy. Results show a low density of bottlenose dolphins, and a rapid decline in common dolphin numbers and encounter rates. I constructed an ecosystem model using Ecopath with Ecosim for the northeastern Ionian Sea to explain the two different abundance trends of these species of dolphins, and the trophic interactions with their prey and with the fisheries. The Ecopath model was built for the year 1964, adding data on biomass, P/B, Q/B and diet for each functional group of the ecosystem, fisheries landings and discards. Ecosim was used to generate simulated trajectories to fit with the ‘observed’ trends (e.g., biomass, bycatch, CPUE and catches) for the most important groups of the ecosystem. The results of the fitting underline a clear decline of common dolphins caused by reduced prey availability. In particular, sardine and anchovy stocks, the main prey of common dolphins, have decreased sharply since the late 1970s due to intensive fishing pressure in the area until the end of 1990s. On the other hand, the population of bottlenose dolphins has increased through time; a positive correlation was observed between this species of dolphin and the development of the fish farm industry in the study area. The Ecopath model suggested that this increase could be attributed to an increase in productivity in the waters that surround the fish cages in the study area. Ecosim was used to simulate three fishing policy scenarios within the study area. Three different fishing closures were investigated: the closure of purse seiners; the closure of the industrial fisheries (purse seiners, trawlers and beach seiners); and the closure of the entire fishing fleets. According to Ecosim predictions, sardines and anchovies would benefit from all three management strategies. Common dolphins showed a significant increase only when the entire study area was closed to fishing. The creation of MPAs was explored using Ecospace. In particular, two different scenarios were evaluated: a MPA1 that closed the entire area to fisheries, and a MPA2 that allowed the small and big artisanal fisheries to operate. The results obtained using this spatial model agreed with similar scenarios simulated in ii Ecosim. The application of Ecopath with Ecosim and Ecospace appeared to be a useful tool for understanding this marine ecosystem. The models underlined the management actions needed to restore and protect common dolphins, bottlenose dolphins and other target species. In particular, measures to reduce overfishing, stop illegal fishing activities and to enforce existing laws are needed. Implementing marine protected area seemes to be an effective management measure to ensure prey survival and sustain marine predators such as common dolphins. iii Table of contents Abstract ............................................................................................................... ii Table of contents............................................................................................... iv List of tables ...................................................................................................... vi List of figures.................................................................................................... vii Acknowledgements ............................................................................................ x CHAPTER 1: INTRODUCTION............................................................................ 1 1.1 Fisheries in the Mediterranean.................................................................... 1 1.2 Marine mammals-fisheries interactions....................................................... 1 1.2.1 Interactions fisheries-marine mammals in the Mediterranean Sea ....... 3 1.3 Marine Protected Areas .............................................................................. 4 1.4 Ecosystem based-approach modeling ........................................................ 5 1.5 Study area: the Northeastern Ionian Sea .................................................... 6 1.6 The cetaceans of the Ionian Sea................................................................. 8 1.6.1 Key species: the short-beaked common dolphin .................................. 8 1.6.1.1 Description and distribution............................................................ 8 1.6.1.2 Diet................................................................................................10 1.6.1.3 Interaction with fisheries................................................................10 1.6.1.4 Conservation status ......................................................................11 1.6.2 Key species: the common bottlenose dolphin......................................12 1.6.2.1 Description and distribution...........................................................12 1.6.2.2 Diet................................................................................................13 1.6.2.3 Interaction with fisheries................................................................13 1.6.2.4 Conservation status ......................................................................14 1.7 The fisheries of the northeastern Ionian Sea..............................................14 1.8 Objectives and aim of the study .................................................................17 CHAPTER 2: METHODOLOGY..........................................................................18 2.1 The input parameters .................................................................................18 2.2 Functional group description ......................................................................19 2.2.1 Short-beaked common dolphins .........................................................19 2.2.2 Common bottlenose dolphins .............................................................20 2.2.3 Mediterranean monk seal ...................................................................21 2.2.4 Sea birds .............................................................................................23 iv 2.2.5 Loggerhead turtle ...............................................................................24 2.2.6 Tuna ....................................................................................................25 2.2.7 Swordfish.............................................................................................26 2.2.8 Sardines ..............................................................................................27 2.2.9 Anchovy...............................................................................................29 2.2.10 Other pelagics ...................................................................................29 2.2.11 Hake ..................................................................................................30 2.2.12 Other demersals ................................................................................31 2.2.13 Pen-associated planktivores..............................................................32 2.2.14 Cephalopods .....................................................................................33 2.2.15 Crustaceans ......................................................................................34 2.2.16 Benthic invertebrates.........................................................................35 2.2.17 Zooplankton and pen-associated zooplankton ..................................35 2.2.18 Phytoplankton and pen-associated phytoplankton ............................36 2.3 Fisheries parameters .................................................................................37 2.3.1 Discards...............................................................................................40 2.4 Ecopath with Ecosim..................................................................................40 2.4.1 Ecopath ...............................................................................................41 2.4.2 Ecosim.................................................................................................41 2.4.3 Ecospace.............................................................................................44 CHAPTER 3: RESULTS .....................................................................................46 3.1 Balancing the 1964 model..........................................................................46 3.2 System productivity (nutrient forcing function)............................................53 3.3 Time-series fitting.......................................................................................53 3.4 Fishing closures scenarios.........................................................................67 3.5 Ecospace ...................................................................................................74 CHAPTER 4: DISCUSSION................................................................................79