The Ecology, Distribution and Spawning Behaviour of the Commercially Important Common Cuttlefish (Sepia officinalis) in the Inshore Waters of the English Channel

Reduced file size version uploaded on 31.10.19 by LW (LED)Over the last 50 years there has been a rapid increase in global landings of cephalopods (octopus, squid and cuttlefish). In European waters, cuttlefish are among the most important commercial cephalopod resources and within the North-East Atlantic, the English Channel supports the largest cuttlefish fishery, with the common cuttlefish, Sepia o cinalis (Linnaeus, 1758), dominating landings. S. o cinalis has a short (2 year) life cycle in the English Channel that is punctuated by seasonal migrations inshore and o shore. Using a combination of di erent métiers including beam trawling, otter trawling and coastal trapping, this shared fisheries resource is targeted at nearly every phase of the life cycle. Despite this continuing increase there remain only minimal management measures in place, with no quotas, no total allowable catches, no closed areas, no minimal landing size and no routine assessment of stocks. In order to provide sustainable fisheries management advice for S. o cinalis populations it is essential that a thorough understanding of the ecology and life history of this species, in particular the factors a ecting spawning and recruitment variability, is attained.In this thesis, I examine critical gaps in our understanding of the distribution, movements, habitat use and behaviours of spawning and sub-adult S. o cinalis. This research provides baseline data for this species within the inshore waters of the English Channel and uses a combination of novel field-based electronic tracking techniques, in situ subtidal observations of spawning patterns within natural environments and presence-only species distribution modelling. A maximum entropy (MaxEnt) modelling approach was used to predict the distribution of benthic egg clusters using presence-only data. The model showed very good performance in terms of predictive power and accuracy (test area under the receiver operating characteristics curve [AUC] = 0.909) and among the explanatory variables used to build the model, depth (gain = 1.17), chlorophyll-a concentration (used here as a proxy for turbidity; gain = 1.06) and distance from coastline (gain = 1.02) were shown to be the greatest determining factors for the distribution of S. o cinalis spawning. As part of the model output, maps (logistic and binary) of the predicted spawning distribution of S. o cinalis within the English Channel were produced.Subtidal observation were undertaken at spawning grounds on both the North and South coast of the English Channel to investigate spawning habitat and structure use. A total of 15 types of natural spawning structures were identified. The range of spawning structures used varied among sites with Zostera marina identified as the dominant spawning structure at two of the UK sites (Torbay and Poole Bay), potentially indicating a ‘preference’ for this structure within localities. Fractal dimension analysis of the seagrass beds at Torbay revealed that the spatial dynamics of seagrass beds within this site varied significantly between 2011 and 2012 (Mann- Whitney U: Z = 4.92, P < 0.0001) as a result of both anthropogenic and natural disturbance. Interannual changes in the spatial dynamics of these beds could a ect the annual pattern and intensity of spawning at a site. The use of structures with small diameters was found to occur, with cuttlefish adapting the device to their requirements by utilising multiple leaves or thalli in order to achieve a suitable diameter for egg attachment, this was evident in their use of both Chorda filum and Z. marina.This research also provided the first data on the fine-scale movements and behaviours of adult and sub-adult individuals, tracked within their natural environments, using electronic tagging methodologies. That expected patterns of short-term spawning site fidelity at a local level were observed in only two individuals, whilst larger scale movements (up to 35 km) along the coastline were observed in three individuals, indicated that a range of behaviours and movement patterns could occur among spawning adults. Similarly varied patterns of site fidelity were also observed in tagged sub-adults, tracked over an extended period (up to 73 days), using a static acoustic array. These results highlight the complex range of patterns and plasticity in behaviour that exist within natural populations.In summary, a series of di erent approaches was used within this thesis in an e ort to improve our understanding of the fine-scale movement, behaviours and habitat use of S. o cinalis (in both spawning adults and non spawning sub-adults), as well as their potential spawning distribution within the inshore waters of the English Channel. Observing the movements and behaviours of small marine animals like S. o cinalis in their natural environments has traditionally been di cult. Recent developments in technologies and techniques however, including those used within this thesis (e.g. electronic tagging), have highlighted the potential capacity of novel tools to monitor the in situ movements and behaviour of cuttlefish. By providing important insights into the ecology of this species these new tools can aid conservation and management advice for this important commercial fishery species, both within the English Channel and further afield.Marine Biological Association of the United Kingdom; EU Interreg IV funded

The complexities and challenges of conserving common whelk (Buccinum undatum, L.) fishery resources: Spatio-temporal study of variable population demographics within an environmental context.

The commercial fishery for common whelk (Buccinum undatum L.) has expanded significantly in the Irish Sea since 1990 and continues to grow, particularly in Welsh waters and the Isle of Man territorial sea, with landings throughout the region increasing by 227% between 2011 and 2016. Whilst whelk populations are known to be vulnerable to localised overexploitation due to inherent life-history parameters, fisheries remain relatively unrestricted by conservation measures in comparison to other fisheries operating in the area. With the exception of the northernmost fishing ground between the Isle of Man and Scotland (Point of Ayre), the size-at-maturity (L50) estimate for populations sampled during peak-aGSI (the months in which adjusted gonadosomatic index is highest) indicates that whelk are being fished before the time at first spawning throughout the study area. A correlation was detected between the size (total shell length) and depth, with smaller whelks found in deeper waters where there generally is greater fishing effort, although effort data is not available at a resolution to investigate this relationship quantitatively. No clear link between benthic infauna biomass and the average size (total shell length) or reproductive capacity (aGSI) of whelk sampled throughout ICES Area VIIa was found, indicating that the ecological energetics of whelk populations are more likely to be a function of scavenging opportunities than predation on benthic communities. A mixed cohort analysis utilized length-based data to infer a size-at-age relationship in the absence of direct age observations (e.g. statolith rings), with whelk recruiting into the Isle of Man fishery five years after hatching. The evidence presented in this study suggests that, prior to recommending a MLS that will adequately protect the spawning stock biomass, L50 values should be adjusted for pre-spawning growth between the ideal time of assessment (when aGSI values are at a peak) and the spawning season (when aGSI values decrease).No Full Tex

Effect of temperature on the growth of the commercially fished common whelk (Buccinum undatum, L.): a regional analysis within the Irish Sea

In response to increased demand in Asian markets, the commercial fishery for the common whelk (Buccinum undatum, L) has expanded in north-eastern Europe. In the Irish Sea region (ICES Area 20 VHa), increased effort and landings have raised concerns about long-term stability of the fishery amongst stakeholders. Fisheries in Welsh waters and the Isle of Man territorial sea are now subject to an increased minimum landing size according to the best available scientific data. This study addresses key knowledge gaps by investigating the size-at-age relationship of the species across the latitudinal extent of the fisheries management region. Our findings show that growth parameters, modelled using growth rings observed in the statolith, vary between populations and show a broadly latitudinal pattern. Thermal-time (expressed as sea bottom temperature degree-days) showed a significant negative linear relationship with the asymptotic size reach by whelk populations (L-infinity), where whelk grew to a larger maximum size in cooler waters. Other parameters, including maximum growth rates and the age at which growth rate begins to decrease, showed clear trends with sea-bottom temperature but linear modelling failed to detect significant relationships, where warmer waters increase the rate of growth in the early life stages of whelk but cooler waters allow growth to continue until later in life. Whilst there are substantial requirements to further validate and refine the relationship between growth and sea-bottom temperature, extrapolation of these data to other regions in Northeast Europe may provide a valuable tool in approximating important life-history characteristics in stock assessments, such as L-infinity, age-at-L-50 and age-at-recruitment

A review of the factors influencing spawning, early life stage survival and recruitment variability in the common cuttlefish (Sepia officinalis)

Global landings of cephalopods (cuttlefish, squid and octopus) have increased dramatically over the past 50 years and now constitute almost 5% of the total world’s fisheries production. At a time when landings of many traditional fin-fish stocks are continuing to experience a global decline as a result of over-exploitation, it is expected that fishing pressure on cephalopod stocks will continue to rise as the fishing industry switch their focus onto these non-quota species. However, long-term trends indicate that landings may have begun to plateau or even decrease. In European waters, cuttlefish are among the most important commercial cephalopod resource and are currently the highest yielding cephalopod group harvested inthe north-east Atlantic, with the English Channel supporting the main fishery for this species. Recruitment variability in this short-lived species drives large fluctuations in landings. In order to provide sustainable management for Sepia officinalis populations, it is essential that we first have a thorough understanding of the ecology and life historyof this species, in particular, the factors affecting spawning, early life stage (ELS) survival and recruitment variability. This review explores how and why such variability exists, starting with the impact of maternal effects (e.g. navigation, migration and egg laying), moving onto the direct impact of environmental variation on embryonic and ELSs and culminating on the impacts that these variations (maternal and environmental) have at a population level on annual recruitment success. Understanding these factors is critical to the effective management of expanding fisheries for this species

A method for long-term electronic tagging and tracking of juvenile and adult European common cuttlefish Sepia officinalis

The physiology and behaviour of captive cuttlefish have been well studied over recent decades and yet very few parallel studies have investigated the movements and behaviour of free-ranging animals. One reason for this gap is that methods for longer term tracking are not well developed for the majority of species, especially those of smaller size. In this study we describe a methodology for the long-term attachment of electronic tags to free-ranging cuttlefish of a broad size range. Five common cuttlefish Sepia officinalis (122–240 mm mantle length) were fitted with temperature and depth-logging archival tags attached to the internal cuttlebone of the living animal (tag weight was &lt; 1.8% of body weight). Tagged animals recovered rapidly from sedative and surgical procedures and resumed feeding within 24 h of tag attachment. Laboratory-kept cuttlefish maintained in a 2-m deep aquarium exhibited diel vertical movements, spending daylight hours close to the bottom and ascending into the water column at night, a behaviour which is consistent with normal diel vertical migration seen in other marine organisms such as zooplankton and fish. That regular feeding and expected patterns of depth use were observed indicates that tag attachment did not impede normal behaviours. Furthermore, tags remained attached to laboratory cuttlefish for up to 5 months, from first tagging through to natural mortality, and with the tag remaining attached to the cuttlebone post mortem. We also found that cuttlebones with attached tags remained buoyant at the water's surface post mortem, offering the unique opportunity to recover archival tags from cuttlebones washed ashore. The capacity for long-term attachment to juvenile cuttlefish and recovery following natural mortality identifies the potential of this method for recording near ‘lifetime’ behaviour and movements of cuttlefish in their natural environment