Using opportunistic data to study the distribution and abundance of a warm water elasmobranch at the northern edge of its range

Detecting changes in the distribution and abundance of marine species that are cryptic or occurring in very low abundances is difficult, but essential for assessing their status and informing management. One way of quantifying these changes is through the collation of opportunistic records. We reconstruct the population trajectory and distribution of the common stingray Dasyatis pastinaca around Great Britain, using opportunistic records, mostly obtained by recreational anglers. We tested if D. pastinaca declined in abundance and body size in response to fishing and if their distribution has shifted northwards in response to warming seas. We obtained 518 records covering the period 1838-2020. After correcting for observation effort, D. pastinaca catches reported by anglers showed no long-term trend over 50 years, but with a decrease from 1970-1995 and an increase in abundance since 1995. While records of species occurrence were found around much of Great Britain, nearly all were from south of 54° latitude, and records have contracted southwards since 2000. No trend in maximum size through time was detected. In conclusion, we did not find support for the hypothesized declines in abundance and body size or a northward shift in distribution of D. pastinaca and instead found a southward contraction

A Path to a Sustainable Trawl Fishery in Southeast Asia

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Near Disappearance of the Angelshark Squatina Squatina Over Half A Century of Observations

Marine extinctions are particularly difficult to detect and almost all have been discovered after the fact. Retrospective analyses are essential to avoid concluding no-extinction when one has occurred. We reconstruct the Angelshark population trajectory in a former hotspot (Wales), using interviews and opportunistic records. After correcting for observation effort and recall bias, we estimate a 70% (1.5% yr-1) decline in abundance over 46 years. While formerly widespread, Angelshark distribution contracted to a central core of Cardigan Bay. Angelshark declined almost unnoticed in one of the best-monitored and most intensively managed seas in the world. Bycatch may be minimised by limiting netting on shingle reefs in Cardigan Bay. We provide the first quantitative time series to reveal the timing and trajectory of decline of Angelshark in the coastal waters of Wales and uncover historical centres of abundance and remnant populations that provide the first opportunity for the focus of conservation.&nbsp

Vertical migrations of fish schools determine overlap with a mobile tidal stream marine renewable energy device

Large increases in the generation of electricity using marine renewable energy (MRE) are planned, and assessment of the environmental impacts of novel MRE devices, such as kites, are urgently needed. A first step in this assessment is to quantify overlap in space and time between MRE devices and prey species of top predators such as small pelagic fish. Here, we quantify how the distribution of fish schools overlaps with the operational depth (20–60 m) and tidal current speeds (≥1.2–2.4 m/s) used by tidal kites, and the physical processes driving overlap. Fish schools undertake diel vertical migrations driven by the depth of light penetration into the water column, controlled by the supply of solar radiation and water column light absorption and scattering, which in turn depends on the cross‐sectional area of suspended particulate matter (SPM). Fish schools were found shallower in the morning and evening and deeper in the middle of the day when solar radiation is greatest, with the deepest depths reached during predictable bimonthly periods of lower current speeds and lower cross‐sectional area of SPM. Potential kite operations overlap with fish schools for a mean of 5% of the time that schools are present (maximum for a day is 36%). This represents a mean of 6% of the potential kite operating time (maximum for a day is 44%). These were both highest during a new moon spring tide and transitions between neap and spring tides. Synthesis and applications. Overlap of fish school depth distribution with tidal kite operation is reasonably predictable, and so the timing of operations could be adapted to avoid potential negative interactions. If all interaction between fish schools was to be avoided, the loss of operational time for tidal kites would be 6%. This information could also be used in planning the operating depths of marine renewable energy (MRE) devices to avoid or minimize overlap with fish schools and their predators by developers, and for environmental licencing and management authorities to gauge potential ecological impacts of different MRE device designs and operating characteristics