Tides and Moon Drive Fish Movements in a Brackish Lagoon T ∗ Marco Milardi , Mattia Lanzoni, Anna Gavioli, Elisa Anna Fano, Giuseppe Castaldelli
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Estuarine, Coastal and Shelf Science 215 (2018) 207–214 Contents lists available at ScienceDirect Estuarine, Coastal and Shelf Science journal homepage: www.elsevier.com/locate/ecss Tides and moon drive fish movements in a brackish lagoon T ∗ Marco Milardi , Mattia Lanzoni, Anna Gavioli, Elisa Anna Fano, Giuseppe Castaldelli Department of Life Sciences and Biotechnology, University of Ferrara, Via Luigi Borsari 46, Ferrara, 44121, Italy ARTICLE INFO ABSTRACT Keywords: Brackish lagoons, on the edge between marine and freshwater ecosystems, are vulnerable aquatic environments Moon that act as nursery grounds for several of the most commercially exploited fish families. We used long-term Tide passive gear data, to investigate whether the moon and tides affected fish movement between inner and outer Shallow lagoon habitats in a Northern Mediterranean coastal lagoon. In particular, we used multivariate, threshold and non- Juvenile fishes linear correlation analyses to explore the relationship between fish catches and moon and tide variables in Movement transitional habitats, accounting for the presence of potential prey and other major temporal and environmental Grey shrimp variables. Fish movements between habitats were influenced by moon and tide factors, which had effects comparable to annual and seasonal variations, respectively. Overall, the magnitude of effects related to the moon parameters were smaller than most environmental parameters examined, but still larger than e.g. the presence of invertebrate prey (lagoon shrimp) or some of the tide factors. European flounder catches were positively cor- related with disk illumination, while sand and black goby were influenced by the moon phase. Other benthic and pelagic species showed no significant correlation. Tide direction affected negatively the movement ofboxlip mullet and tide amplitude prior to sampling had far more effect than tide amplitude during sampling. Water temperature, salinity and the presence of invertebrate prey (grey shrimp) had significant but contrasting effects on some, but not all, of the species examined. Ultimately, this information could improve the understanding of the drivers in these ecosystem as well as potentially provide useful insights for improved fisheries management. 1. Introduction while much effort has been devoted to investigate the role ofthese habitats in juvenile fish growth (e.g. Tournois et al., 2017), much less is Brackish lagoons are some of the most important and vulnerable known about the factors that affect fish movement between inner and aquatic environments worldwide, sitting on the edge between marine outer lagoon habitats. and freshwater ecosystems (Newton et al., 2014). Their biotopes thrive Fish movement has been traditionally investigated in the field using on a delicate balance between multiple factors where salinity plays a tracking systems, which can identify the position of single individuals key role (Blaber and Blaber, 1980; Gelin et al., 2001; Young et al., equipped with passive or active transmitters to a certain degree of 1997). Some species have adapted specifically to this balance and precision (Abecasis and Erzini, 2008; Gonzalez and Gerlotto, 1998; complete their whole life cycle in coastal lagoons (e.g. the sand goby Hussey et al., 2015). Alternatively, some insights could also be derived Potamoschistus minutus, Leitão et al., 2006). However, both marine and through the capture of individuals with passive fishing gear, provided freshwater fish species can temporarily inhabit lagoons, when theen- that the gear is operated in a suitable position (i.e. on movement routes, vironmental conditions allow their presence (Franco et al., 2008). e.g. channels between different habitats). This is very well known to Furthermore, brackish lagoons constitute nursery grounds for several of fishermen, who traditionally set their gears in these positions inan the most commercially exploited families of marine fish such as attempt to maximize their catches. Some insights could be derived from Pleuronectidae, Sparidae or Clupeidae (Tournois et al., 2017). Juvenile catches and traditional knowledge but fishermen's knowledge has not fishes might reside in coastal lagoons for a variable amount oftime, yet been fully recognized as relevant for the management of marine fish since some of the lagoon habitats can provide abundant prey and refuge resources (Johannes and Hviding, 2000). Among this traditional from predators (Beck et al., 2001). Yet, despite their reduced movement knowledge, there is a wealth of contrasting theories about the effects of capabilities, juveniles can and will move from one habitat to the other the moon and tides, which are yet to be thoroughly investigated. Per- within the lagoon to capitalize on the available resources (Verdiell- haps the most famous is the “Solunar” theory, which is at the origin of Cubedo et al., 2013), often transitioning to coastal waters. However, tables claiming to predict periods of increased fish activity based on ∗ Corresponding author. E-mail address: [email protected] (M. Milardi). https://doi.org/10.1016/j.ecss.2018.09.016 Received 22 June 2018; Received in revised form 7 September 2018; Accepted 17 September 2018 Available online 18 September 2018 0272-7714/ © 2018 Elsevier Ltd. All rights reserved. M. Milardi et al. Estuarine, Coastal and Shelf Science 215 (2018) 207–214 lunar, tidal and solar information (Knight, 1942). Moon cycles are supposed to affect catches through an influence on the behavior and movements of fishes (Banks, 1969; Stoner, 2004), but neither their ef- fect nor mechanisms seem to be fully understood. There are multiple ways in which the moon can affect fish move- ment, but these could be simplified in two categories: primary (i.e. gravitational) and secondary (i.e. illumination and tide influence) ef- fects (Kuparinen, O'hara, & Merilä, 2009). Primary effects would as- sumedly be regulated by the presence/absence of the moon in the sky, while secondary effects would also be modulated by the moon phase (waxing or waning) and the disk illumination (Battaglia et al., 2017; Griffiths, 1999; Kuparinen et al., 2010). The moon cycle and its position in the sky can also affect tides: tides move water in and out ofthe lagoon, therefore potentially exerting a strong influence on juvenile fishes, which are poor swimmers and might be dragged by tidal currents but could also be adapted to exploit these currents to move between different foraging grounds (Bennett et al., 2015; Childs et al., 2008; Næsje et al., 2012). Some of these effects have been recognized as re- Fig. 1. Map showing the location of the Fattibello Lagoon and its area, as well levant factors in fisheries catches (Pulver, 2017), and it has been sug- as the sampling point (red dot) and location of the water chemistry and tide gested that they could potentially affect our estimates of population size probes (blue dots). (For interpretation of the references to color in this figure (Stoner, 2004). legend, the reader is referred to the Web version of this article.) The Mediterranean Sea could be a prime ground to test whether fishermen knowledge on moon and tides reflects actual patterns inju- depth 1 m). The lagoon substrate is also very variable, including muds venile fish movement between marine and brackish habitats. Inthis and silts as well as sands and harder substrates (mussel beds, shell area, coastal lagoons are prime nursery areas for juvenile fish and have hash). Water currents reshape the softer sediments, sometimes creating also been the focus of extensive ecological research and environmental temporally shifting patterns of sandbars. The average tidal event in this monitoring (e.g. Aschonitis et al., 2017; Franco et al., 2006; Zucchetta area has a magnitude of approximately 40 cm, but tidal range is rather et al., 2010), creating ideal conditions for further research. The Fatti- variable (5–90 cm tidal amplitude). bello Lagoon, in the Northern Adriatic Sea, hosts a long-standing fishing The high habitat complexity and variability, as well as the con- tradition with lift nets along channels, which could act as fish pathways nection to the sea, make this lagoon an ideal nursery for several fish both within the lagoon and between the freshwater and marine en- species of commercial interest, including European eel, European vironments. We thus used traditional passive fishing gear operated in flounder, European seabass and gilthead seabream. channels to gauge fish presence in transitional habitats of a coastal lagoon in northern Italy. Based on local fishermen knowledge, we hy- pothesized that both moon and tides would have a significant effect on 2.2. Fish sampling the movement of fish between marine and brackish habitats, with new moon and rising tide constituting the best conditions for movement. A total of 32 fish sampling events were carried out over the spanof6 Specifically, we hypothesized that new moon phases would favor the years, between 2009 and 2014 (Table 1). Sampling events were not movement of fish during the day and that marine fishes would enter the equally distributed in all years but, in each year, covered at least the lagoon on flooding tides. We used multivariate, threshold and non- relevant seasons when juveniles of marine species are present in the linear correlation analyses to explore the relationship between fish lagoon. In 2011, at least one sampling event was carried out in each catches and moon and tide variables, taking also into account the month, to ensure that the full year spectrum was taken into account. presence of potential prey and other major temporal and environmental Fish sampling was performed using stationary lift nets, a traditional variables. Ultimately, this information would not only test whether fishing method in the area adapted to capture also juvenile individuals. there is a basis for traditional knowledge, but also improve the un- Lift nets are 15 × 15 m square nets with an outer mesh of 12 mm, a derstanding of the drivers in these ecosystem as well as potentially second of 8 mm, and an inner one of 6 mm. Nets are operated from a provide useful insights for improved fisheries management.