Contents lists available at ScienceDirect Ecological Modelling journal homepage: www.elsevier.com/locate/ecolmodel Modelling long-term fisheries data to resolve the attraction versus production dilemma of artificial reefs Ruben H. Roa-Ureta a, ⁎ , Miguel N. Santos b , Francisco Leitão c a King Fahd University of Petroleum and Minerals, Center of Environment and Water, 31261, Dhahran, Saudi Arabia b Instituto Portugues de Mar e da Atmosfera, Avda. 5 de Outubro s/n, 8700-305 Olhão, Portugal c Centro de Ciências do Mar, Universidade do Algarve, Campus de Gambelas, 8005-139, Faro, Portugal ARTICLE INFO Keywords: Artificial reefs Environmental carrying capacity Attraction versus production Model Stock assessment Small-scale fishery Portugal ABSTRACT The main role of artificial reefs (ARs) is to enhance the productivity and sustainability of coastal fisheries by creating new fish biomass. From a modelling point of view, the creation of new fish biomass would be realized by a shift to a state of higher carrying capacity of the environment (K) for aquatic populations and communities. However, it has not been possible to demonstrate unequivocally rising K as a result of AR deployment because of the difficulty in disentangling enhancements due to simple distributional changes (the attraction hypothesis) versus total abundance rise (the production hypothesis). Here we develop a modelling framework based on simple, inexpensive fisheries data to quantify the impact of ARs, disentangling attraction from production by assessing the rise in regional K. The rationale is that if attraction to ARs from the wider region was the main driver of increased abundance in the ARs then regional K would have remained constant before, during and after deployment of the ARs. Therefore an increase in regional K disproves the hypothesis of attraction. The study case is the fishery for the two-banded seabream Diplodus vulgaris in southern Portugal. Monthly time series of 27 years of landings, 20 years of fishing effort, were available from three small-scale fleets: one was the artisanal fleet operating on the ARs and the other two were semi-industrial fleets operating on the wider continental shelf. The model that we developed and applied incorporated the data from all fleets so it evaluated the change in regional K. We show that regional K for D. vulgaris increased by 35% after final deployment of the ARs and it did so in linear fashion during four years. From a fisheries perspective the result was more nuanced because although the deployment succeeded in raising regional K, stock biomass and thereby enhancing the artisanal fishery, it also led to a substantial rise in total fishing mortality and exploitation rate because the semi-industrial fleets oper- ating offshore increased their harvest rate nearly 3-fold. Our modelling framework has wide applicability in other regions due to the elementary nature of the necessary fishing monitoring data. 1. Introduction Thousands of artificial reefs (ARs) have been deployed around the world, both in marine and fresh waters, since their first use for the enhancement of coastal fisheries in Japan in the late 18th century (Stone et al., 1991). Enhancement of coastal fisheries by ARs may happen because of distributional changes of the existing biomass, i.e. attraction of fish to ARs, and/or because of rising abundance, i.e. the production of new fish biomass in the ARs in addition to the existing regional biomass. Disentanglement of the relative contribution of dis- tribution and abundance to ARs coastal fisheries enhancement has been the subject of intense study and debate (Bohnsack, 1989; Lindberg, 1997; Pickering and Whitmarsh, 1997; Grossman et al., 1997) because if ARs merely aggregate fish from surrounding areas then in the short term fisheries output can be enhanced but in the long term the net effect on fisheries sustainability may actually be detrimental (Grossman et al., 1997). One approach to support the hypothesis that new production of biomass in the ARs enhances fisheries in a sustainable manner is to evaluate biomass before, during and after AR deployment simulta- neously over the ARs and over the regional, wider ecosystem (Carr and Hixon, 1997). Production of new biomass due to AR deployment relies on the assumption that a latent biological productivity does not materialize because hard-substrate habitat is a limiting factor. AR surfaces and 3D structure would channel some of the latent potential into new ecolo- gically viable habitat (Broughton, 2012). From a modelling point of view the overall effect would be that environmental carrying capacity (K) rises, leading to higher abundance and biomass of marine biota. https://doi.org/10.1016/j.ecolmodel.2019.108727 Received 25 February 2019; Received in revised form 19 June 2019; Accepted 20 June 2019 ⁎ Corresponding author. E-mail addresses: ruben@kfupm.edu.sa (R.H. Roa-Ureta), mnsantos@ipma.pt (M.N. Santos), lrabaoui@kfupm.edu.sa (F. Leitão). Ecological Modelling 407 (2019) 108727 0304-3800/ © 2019 Elsevier B.V. All rights reserved. T