Ship Strike Risk for Fin Whales (Balaenoptera physalus) Off the Garraf coast, Northwest Mediterranean Sea

Abstract

Ship strikes are a widespread conservation issue for many cetacean species globally. Population level impacts depend on the occurrence and severity of collisions, which may lead to life altering injuries or fatalities. Such impacts are a major concern for large, long-lived, and reproductively slow species like the fin whale. Since 2014, a seasonal feeding aggregation of fin whales has been monitored from February to June off the Catalan coast (Spain), in the northwest Mediterranean Sea. Oceanographical factors influence the occurrence and high density of krill within submarine canyons along the continental shelf, resulting in high whale abundance within a small spatial area. The study area extends 37 km offshore across a 1,944 km2 marine strip situated between the towns of Torredembarra and Castelldefels. This fin whale feeding ground is exposed to high density marine vessel traffic, given its location between the northern Mediterranean shipping lane, which links Barcelona and Tarragona Ports to the Atlantic Ocean and wider Mediterranean Basin. Ship strikes represent the greatest conservation threat for fin whales in the Mediterranean Sea. At least four fin whales have been found dead in Barcelona Port since 1986 due to ship strikes and seven live whales have been documented with injuries in the study area since 2018. Fin whale distribution was mapped with known high-risk marine vessels’ (cargo, tanker and passenger vessels) shipping lanes. Vessel density and shipping lanes characterised by speed were considered. Collision risk was estimated monthly based on the predicted fin whale occurrence and traffic density. Several shipping lanes crossed the fin whale feeding habitat every month with an average speed of 15 kn. Cargo vessels displayed the highest ship-strike risk during April, overlapping with the peak of fin whale sightings in the critical feeding area. Slower vessel speeds (8 kn) in waters <200 m depth or along the continental shelf should be implemented along the Catalan coast, during the whale season. These suggestions should be applied into the Barcelona Port transport separation scheme. Ship strike risk for this species will persist unless active management plans are adapted in the region to mitigate its risk.

Targeting fin whale conservation in the North-Western Mediterranean Sea: insights on movements and behaviour from biologging and habitat modelling

“…This coincides with the regular observation of high numbers of fin whales along the Catalan coast in the spring months [34]. The Gulf of Lion presents similar oceanographic characteristics: the canyon-rich area allows for intense frontal and eddy activity at the continental shelf edge, when the water mixes with the open sea [34,43]. Moreover, the influx of nutrient-rich waters from the Rhone River makes the area highly productive with strong chlorophyll-a fronts, sustaining large aggregations of Northern krill [44,45].…”

“…The geomorphology of the area, in combination with the main current regimes, promotes primary production and results in high densities of Northern krill Meganyctyphanes norvegica, fin whales' main prey, along the shelf edge in spring [ 18 , 43 ]. This coincides with the regular observation of high numbers of fin whales along the Catalan coast in the spring months [ 34 ]. The Gulf of Lion presents similar oceanographic characteristics: the canyon-rich area allows for intense frontal and eddy activity at the continental shelf edge, when the water mixes with the open sea [ 34 , 43 ].…”

“…Open Sci. 11: 231783 edge, when the water mixes with the open sea [34,43]. Moreover, the influx of nutrient-rich waters from the Rhone River makes the area highly productive with strong chlorophyll-a fronts, sustaining large aggregations of Northern krill [44,45].…”

“…This region hosts some of the busiest traffic lanes in the world (approx. 30% of commercial shipping worldwide [ 25 ]), with the highest risk of collision posed by cargo vessels and, particularly, passenger ferries cruising at relatively high speeds (10–20 knots) [ 34 ]. To mitigate these threats, a suite of different management tools have been developed in the North-Western Mediterranean Sea ( figure 1 ): the Pelagos Sanctuary for Mediterranean Marine Mammals Specially Protected Area of Mediterranean Importance (SPAMI) (hereafter ‘Pelagos Sanctuary'; [ 35 ]); the Cetacean Migration Corridor SPAMI; the North-Western Mediterranean Sea, Slope and Canyon System Important Marine Mammal Area (hereafter ‘NW Mediterranean IMMA'; [ 36 , 37 ]); and the North-Western Mediterranean Sea Particularly Sensitive Sea Area (hereafter ‘NW Mediterranean PSSA'), recently established by the International Maritime Organization (IMO; [ 38 ]).…”

“…Fin whales congregate in the waters of the Corso-Liguro-Provençal basin and the Gulf of Lion [ 18 , 40 ] as the main summer feeding grounds and, in the last decade, they have also been consistently reported in the Catalano-Balearic Sea in spring [ 34 ]. However, it has never been assessed where or how these whales move after leaving this spring area.…”