Most of the boats interacted with are sailboats, both monohulls (72%) and catamarans (14%), although interactions with motor boats (6%), semi-rigid boats (5%) and fishing boats (barely 3%) were also recorded.

Of all these boats, the most common type of rudder was the shovel (in 67% of cases), followed by the overhang (in 22%) and finally the hinged one (barely 1%). In semi-rigid boats and some motor boats, the motor is outboard (approximately 10% of cases) so the movement of the boat is controlled by the movement of the motor and not by an independent rudder.

The most common rudder among modern commercial sailboats is the paddle rudder, present on monohulls and catamarans, at the same time it is the weakest since it is normally made up of two joined plates filled with polyurethane on a shaft, or wick, which goes middle of the blade, still with reinforcements, but not reaching its distal end.

Table. Relationship between the type of rudder of the vessels interacted with by killer whales and the type of damage caused, the percentages are calculated on the total of each type of rudder. Severe damage means not being able to sail, regardless of the extent of the damage. Rudder: a) spade, b) overshot, c) hinge.

The average size of the boats involved was 12 meters, although there are differences depending on each type of boat, in the case of sailboats, they are medium-sized boats, and curiously they are not the most commonly registered in Spain, they sailed at an average of 5.7 knots. The vessels interacted with at that time sailed both under sail and by motor, and no specific color pattern has been detected that is more or less attractive to the killer whales, it is not recognized as a reason for reinforcing their behavior, since all the hull colors have been interacted with.

We highlight the special case of the interactions in the Algarve, where the majority were with small semi-rigid boats, which are the most common among whale watching companies in the area. In this case the interactions consist of physical contact with the floats.

Table. Characteristics of vessels interacted by killer whales since 2020, mean and range

in brackets of length in metres, and speed in knots.

Damage and malfunctions

As described above, not all boaters who have had an interaction or sighting of killer whales report the situation. Although it is considered that the vast majority do so, the exact proportion of those who do not report is unknown. Of all the cases recorded, and thanks to the efforts made to collect this information, it is possible to state that 10% of the sailors involved in interaction episodes provided incomplete information, while in 90% of the cases we have details of the interaction, malfunctions and their magnitude.

In this sense, it is known that in 40% of the cases, the ships interacted with had no consequences, damage or damage. In the same way, it can be stated that, among those that showed damage (50% of the cases), 60% were minor and, although they were of different nature, they did not impede navigation in any case. However, the remaining interactions with damage or malfunctions (40%) were considered serious, i.e. they prevented navigation and had to be towed away. Serious damage included broken rudders, which are the most serious cases in terms of damage, or small internal gear failures that prevented the normal rotation of the rudder and, therefore, the manoeuvrability of the vessel. It collects information on cases with damage, or not, and the type of damage (minor or serious), between 2020 and 2021.

 

If we estimate the number of serious damages in relation to the total number of records (sightings and interactions), serious damages, i.e. those that prevent navigation, account for only 14% of all records in the two years, reaching 15% in 2021, a percentage that is increased by a higher number of interactions, but fewer sightings.

Table. Summary of information with/without damage, as well as the type of damage,

between 2020 and 2021. Percentages calculated over the respective years

Table. Summary of killer whale records, both sightings and interactions

with vessels since 2020, with respect to damage.

An external reference for the number of incidents can be the Mini transatlantic single-handed transatlantic race (https://www.minitransat.fr/fr/), in which at least 90 boats sailed in Galician waters from 28 September to 4 November, coinciding with the killer whales' northward ascent (Figure 28). Four boats in the race were interacted and only one of them was significantly damaged, which would mean that 4% of all boats were interacted, resulting in serious damage to 25% of the boats interacted, but only 1% of all boats participating in the event. However, this is a very inaccurate estimate, given that there were probably other unreported interactions with other boats and because we do not know the actual number of boats that could have been in the area during those days, which could have exceeded three times the number of boats in the regatta.

In many testimonies it was recorded that the killer whales pushed the boat, accelerating the speed of the boat, pushing it forward. This pushing was carried out either when the ship was moving or when the ship was stationary, so that the killer whales push the ship regardless of the speed of the ship. This behaviour has no consequences in terms of damage or damage, unless it is carried out under the rudder, after having previously bent the rudder stock (its metal shaft) sideways, so that the rudder adopts a horizontal position with a surface suitable for pushing.

We checked the consequences of the interactions depending on the behaviour of the crews; we analysed whether or not they followed the safety protocol, whether or not they stopped the vessel, regardless of whether or not they knew or applied the protocol. We consider that the crews did not follow the safety protocol, or did not stop the boat, when they maintained speed, accelerated, or reinforced the behaviour of the killer whales with the aforementioned occurrences. We considered that the crews followed safety protocol when they stopped the vessel.

Graphic. Consequences of interactions depending on the behaviour of vessels with

respect to stopping or not stopping the ship.

The results show that there is a slight association between not stopping the boat (with damage: 51% stop vs. 55% do not stop) and the consequences for the boats, both in terms of damage and serious damage (serious damage: 24% stop vs. 31% do not stop), although the different cases do not show significant differences. That is to say that by stopping the boat, and keeping calm, the boat can be both damaged and not damaged, but when the boat is not stopped and/or the behaviour is reinforced, positively with speed, it seems more likely that the boat will end up with damage and more serious damage. However in 10 cases the interacted ships perform both behaviours, e.g. stop at first, but then start the ship, or the other way around, so the effects of this ship behaviour (stop/no stop) may be mixed. These results need to be corroborated and reinforced by the studies proposed in the pilot study with respect to ship behaviour.

On the other hand, the consequences of the different "techniques" that the boats used to try to deter killer whales during interactions were analysed in more detail. These "techniques" can be either intentional such as the use of bait, flares, diesel, stones and other objects, reversing, releasing black water, shouting to try to deter the animals; or simply the boat already had fishing lines in the water, or music on the boat and their effect on the consequences on the interactions has also been considered.

Graphic. Consequences of interactions depending on the behaviour of vessels

with regard to the use of deterrent "techniques".

Alfredo López Fernández y Ruth Esteban Pavo (Coord). 2021. Elaboración de un estudio científico sobre la interacción de la población de Orca (Orcinus orca) del Estrecho de Gibraltar con embarcaciones para el diseño y propuesta de medidas de prevención, actuación y gestión. Grupo de Trabajo Orca Atlántica-GTOA/Coordinadora para o Estudo dos Mamíferos Mariños-CEMMA y Grupo de Trabajo Orca Atlántica-GTOA. Nombres de los autores. proyecto LIFE INTEMARES. Fundación Biodiversidad.