Miguel N. Santos

Comparison of the catch and fishing yield from an artificial reef system and neighbouring areas off Faro (Algarve, south Portugal)

Abstract In 1990 an artificial reef system, consisting of a protection reef (PR – 735 cubic modules) and an exploitation reef (ER – 20 large concrete modules), was deployed off Faro by the Portuguese Institute of Marine Research (IPIMAR). A gill net survey was carried out over four and a half years to test the effectiveness of the artificial reef in attracting fish assemblages and enhancing fishing yield. The fishing yield (in weight) from the reefs exceeded that from the control sites: 1.86 times for the PR, and 2.28 times for the ER. The mean CPUE of species and the mean CPUE species diversity were also higher at the ER than at the respective control site. The overall conclusion was that the Faro artificial reef system enhances fishing success and the CPUE of benthic species. However, reef deployment did not affect the community equilibrium, since the relative proportion of the different functional groups, that constitute the fish assemblages caught by the gill nets, did not change.

Shell morphometric relationships of the most common bivalve species (Mollusca: Bivalvia) of the Algarve coast (southern Portugal)

This study reports shell morphometric relationships (height/length and width/length) for the most common and abundant bivalve species of the Algarve coast (southern Portugal). The individuals were caught during periodic exploratory fishing surveys carried out during 2000 using artisanal fishing gears (clam dredge and razor clam dredge), on soft bottoms in the subtidal zone down to 25 m depth. For this particular study, a total of 7497 bivalves were sampled, belonging to 25 species distributed in 9 Families. Almost all regressions were significant (P<0.05 = 52%) or highly significant (P<0.01 = 44%), the only exceptions being the W/L relationships for two bivalve species (n.s. = 4%). The results revealed that both for height/length and width/length morphometric relationships most species presented positive allometric growth (H/L = 11 species; W/L = 15 species), followed by isometric growth (H/L = 7 species; W/L = 6 species) and by negative allometric growth (H/L = 7 species; W/L = 4 species). Data were compared with some morphometric relationships available for the same species in other geographical areas and several ecological hypotheses or explanations were formulated for the distinct types of growth exhibited by different bivalve species.

The Olhão artificial reef system (south Portugal): Fish assemblages and fishing yield

Abstract Since 1989 the Portuguese Institute of Marine Research (IPIMAR) has been developing an artificial reef systems pilot project. The artificial reef system consists of a protection reef and an exploitation reef. As part of this project, a fishing survey was carried out over four and a half years, using gill nets. To test artificial reef effectiveness in enhancing fish assemblages and yield, a total of 72 catch operations were made. The fishing yields (weight) from the reefs exceeded those from the control sites, by 2.03 times for the protection reef, and by 1.11 times for the exploitation reef. Artificial reef deployment resulted in an enrichment and diversification of the local fish community, with an increase in the total species richness, mean species richness and the species diversity indices. Since the artificial reefs improved the local fishing yields and made possible a better use of the Ria Formosa ‘nursery potential’, the reefs appear to represent a useful management tool on the Algarve coast, contributing to the improved value of the artisanal fishery, which has a very important role in this region.

A comparison of direct macrofaunal mortality using three types of clam dredges

The white clam Spisula solida is harvested along the entire coast of Portugal using mechanical dredges. In this study, the total direct mortality of the macrobenthic community caused by three types of clam dredges (north dredge—ND, traditional dredge—TD, and the metallic grid dredge—GD) used in the S. solida fishery was determined and compared. The relationship between mortality and catching efficiency for each type of dredge was also assessed. Our results showed significant differences for total direct mortality between the ND and both the GD and TD dredges. This difference was largely attributed to the mortality of animals that died in the dredge track as a direct result of the physical damage inflicted by the dredge passing. It was also found that the damage to uncaught individuals is directly related to gear efficiency. The lower catching efficiency of the ND (64%) led to a higher proportion of damaged individuals being left in the dredge path, when compared with the more efficient GD (98%) and TD (90%) dredges. Short and long-term implications of the impact of dredging on the composition of benthic communities are discussed. From fisheries management and ecological points of view, there are obvious advantages to introduce into the bivalve dredge fisheries more efficient and selective dredges in order to reduce the number of damaged individuals and by-catch, and consequently decreasing the impact on the macrobenthic communities.

Aspects of the biology and gillnet selectivity of the axillary seabream (Pagellus acarne, Risso) and common pandora (Pagellus erythrinus, Linnaeus) from the Algarve (south Portugal)

Abstract Two species of seabreams, Pagellus acarne and Pagellus erythrinus, from the Algarve coast (south Portugal) were studied to obtain information on these fisheries. This study presents results on first maturity, length-weight relationships and gillnet selectivity curves, which may be used to provide a scientific basis for management proposals. Spawning lasts from May to August, and length at first maturity was 20.95 cm for P. acarne and 18.03 cm for Pagellus erythrinus. Males reached first maturity at smaller lengths than females. The relationships between length and weight were W = 0.0085TL3.153 for P. acarne and W = 0.0189TL2.881 for P. erythrinus. The Sechin method was used to determine gillnet selectivity curves. The estimated selectivity curves correspond closely to the catch curves, but were narrower. P. acarne will be caught in the following length ranges: 15–25 cm, 18–27 cm and 20–29 cm, and P. erythrinus in the length ranges 15–25 cm, 16–27 cm and 19–30 cm, respectively, by the 60 mm, 70 mm and 80 mm mesh sizes.

Short-term environmental impact of clam dredging in coastal waters (south of Portugal): chemical disturbance and subsequent recovery of seabed

The physical and chemical changes in sediment and near bottom water caused by clam dredging were examined during July and September 1999, at two locations Vilamoura (VL) and Armona (AR), south coast of Portugal. Sediment cores and near bottom water were collected simultaneously before dredging (control samples) and within short time intervals (min-h) after dredging. After dredging operations, microphytobenthos coming from the path were accumulated in the re-worked sediment (ridge). Chlorophyll a in superficial sediment increased from 1.2 microg x g(-1) before dredging to 1.7 microg x g(-1) after dredging and these higher values remained for a few hours. However, the expected increase of chlorophyll a in near bottom water due to re-suspension was not observed. After sediment disturbance an instantaneous sorption of phosphorus onto iron oxides occurred in the upper sediment layers (from 2 to 3 micromol x g(-1) before dredging to 4-5 micromol x g(-1) after dredging). A microcosm experiment showed that after sediment disturbance HPO(4)(2-) dissolved in pore water decreased from 40 to 10 microM being simultaneously sorbed onto iron oxides formed in the top layer of sediment. The ammonium, nitrates, organic nitrogen, phosphate and silicate dissolved in pore water decreased immediately after dredging activity and simultaneously an increase in near bottom water was sporadically observed. Generally, the re-establishment of seabed was reached within a short time (min-h), at both stations (VL and AR).

A fourteen-year overview of the fish assemblages and yield of the two oldest Algarve artificial reefs (southern Portugal)

Artificial reefs have been deployed worldwide for the last three decades in response to problems concerning coastal resources, ecosystems and fisheries. In many countries they have became important elements of integrated fisheries management plans. In Portugal two artificial reef systems (ARSs) were deployed by the Portuguese Institute of Marine Research (IPIMAR) in 1990, in the southern coast (Algarve). They were located off Faro and Olhao, over different seabottom types and located at different distances from the coastline. To analyse the effect of ARSs deployment on local fish assemblages and to evaluate their effectiveness in terms of mean fishing yields and mean number of species caught, fishing surveys have been conducted over 14 years (256 net sets) using a gillnet to sample the ARS of Faro and Olhao and respective control sites. The fishing yields from the ARs continually exceeded those from the control sites, in both the mean number of species caught and the mean CPUE in weight (1.8–2.6 times); both were higher at Faro. Moreover, the comparison between fish assemblages from the ARS and respective control sites showed that the deployment of the man-made structures did not change the composition of the fish assemblages caught by the gill nets, or the equilibrium of the community, since the relative proportion of the different functional groups of fish remained stable. The ARSs are a useful management tool on the Algarve coast, enhancing and diversifying the catches, thus contributing to improved local artisanal fisheries, which play a major role in this region.

Weight-length relationships of 25 bivalve species (Mollusca : Bivalvia) from the Algarve coast (southern Portugal)

Weight-length relationships of some of the most abundant bivalve species from the Algarve coast (southern Portugal) captured during several exploratory fishing surveys carried out during 2000 on a soft bottom in the subtidal zone down to 25 m depth are reported. For this study a total of 7429 individuals were sampled, belonging to 25 bivalve species in nine families. The most represented families were Mactridae and Veneridae with six species, immediately followed by the families Cardiidae (five species) and Donacidae (three species). The results revealed that most species presented isometric (11 species) or positive allometric relationships (11 species), while only a small minority of species displayed negative growth (three species).

Overview on artificial reefs in Europe

Artificial reefs in Europe have been developed over the last 40 yrs. Most of these reefs have been placed in the Mediterranean Sea, but there is an increasing interest on the part of northern European countries. Fish stock enhancement and fishery management are the main purposes of reef construction in the Mediterranean Sea and on the Atlantic coast of the Iberian Peninsula, while nature conservation/restoration, research, and recreation have been the main purposes served in the other European regions to date. Artificial reef deployment falls under some general regulations concerning the protection of the sea against pollution due to the dumping of unsuitable materials. Specific Regional Plans relating to the use of artificial reefs in the marine environment and Guidelines for reef construction have been derived from these general regulations. In spite of recent developments, national and/or regional programs for the deployment of artificial reefs and/or their inclusion in overall management plans for integrated management of coastal zones are in force only in the majority of Mediterranean countries, while only a few projects have, to date, been undertaken in the other European Regions. Moreover, there is a noteworthy lack of plans, in many countries, for the management of the reefs after their deployment.

Macrobenthic Colonisation of Artificial Reefs on the Southern Coast of Portugal (Ancão, Algarve)

Artificial reef systems play an important role in the increase of natural production of biological marine resources and they have been deployed worldwide. In Portugal, seven artificial systems have been deployed along the southern coast of the Algarve. Research to date has focussed mainly on fish populations, particularly those of economical importance. The present work aims to study the macrobenthic communities of the artificial reef structures, as these will enhance the food resources and shelter, making the reefs more attractive to fish. In particular, we experimentally analysed the sequence of colonisation of macrobenthic communities of the Ancao artificial reef system, which was deployed in the summer of 2002. The study of the colonisation of benthic communities was done using samples of concrete cubic units (15 × 15 cm) that were suspended at the reef modules at a depth of 20 m, at the time of the reef immersion. Four replicate samples were collected by SCUBA diving from two groups of the Ancao reef every three months from the starting date. Sampling was done using essentially non-destructive methods to assess the percentage cover of macrobenthic organisms in both vertical and horizontal surfaces. The percentage cover of the taxonomic groups was compared within the different surfaces of the samples and between the two reef groups. The bottom surface of cubic samples had a significantly higher colonisation related to the dominance of barnacle cover, probably due to lower sedimentation levels. Samples from both reef groups showed a similar pattern of colonisation. Barnacles, bryozoans and serpulids dominated the samples three months immediately after the beginning of the experiment. Other invertebrates groups, such as Porifera, Hydrozoa, Anthozoa, other sessile Polychaeta, Decapoda, Gastropoda and Bivalvia, were more abundant after six months of colonisation.