A by Abigail Alling

When attached to a whale a remora may look like a mon- hat relation exists, then, between a remora and a whale, strous leech, but it is actually a specialized fish, unique in hy are these fish found most often on blue whales? having a powerful sucker on the top of its head. This sucker- Strasburg (1959) examined the stomach contents of disk makes it possible for the remora to attach itself to ecies of remora and concluded that the relation other, larger, marine animals. Scientists speculate that t between remora and host is different for each remora spe- relation is a commensal one (an interaction between two e remora's dependency on a larger animal during organisms where only one benefits without causing the other ontogeny and maturity varies according to the species, as harm) and not mutual or parasitic. But little research on this well as to the type of foods consumed. Some remoras release interaction between fish and whale has been done, and very their suction once the host has captured the prey and is in little is known about the life history, biology, or behavior of the process of consuming it, in order to scavenge on the th "scraps" (foods which are remains of the host's meal, feces, working in the Indian Ocean studying the behavior or skin). Others will obtain a free ride to a feeding site, det- and ecology of sperm whales off the coast of Sri Lanka, I ach themselves, and predate on small mackerel, herring, or saw for the first time a remora attached to a blue whale. plankton. A few are symbionts which remove ectoparasites During this three year study (1982-19841, almost every blue from the host. Each behavior changes slightly the interaction whale we sighted had at least one of these hitch-hikers between host and remora. attached near its blowhole, dorsal fin, or fluke (Fig. 1-4). In The whale-sucker may primarily be a plankton feeder, 1983 I was astounded to see in the film "Whales Weep which could explain why remoras are seldom seen on sperm Not" a blue whale swimming under water with a fleet of and Bryde's whales in Sri Lankan waters. Blue whales feed these animals present on both its lateral and dorsal surfaces. on macroplankton, while sperm whales, which are primarily The other two great whales seen near Sri Lanka, sperm squid and fish eaters, do not eat zooplankton. Although whales and Bryde's whales, were rarely seen with remoras, Bryde's whales may consume zooplankton, they are not the exception being sperm whale calves which occasionally exclusive plankton feeders and they may equally prefer to had remoras attached to their dorsal surface. Probably the feed on small schooling fish. Therefore, a plankton-feeding remora seen on the whales is a whale-sucker, Remilegia aus- remora might select a blue whale as its host rather than a trails. Current evidence indicates that .this species has sperm or Bryde's whale in order to maximize its chances of worldwide distribution in temperate and tropical seas where entering schools of zooplankton. It is also possible that it is found only on cetaceans. In addition, a remora found in remoras are only seen attached to sperm whale calves, and Sri Lankan waters was identified by Gunther in 1960 as not to adults, because the calves do not spend as much time Echneis acutus-a name now synonymous with Remilegia aus- diving as do adults, nor do they reach the extreme depths. A trails. calf would provide a remora with an attachment site, then, Of the eight living remora species, the whale-sucker is the while remaining in the upper productive waters. least studied because it is so seldom collected. Cressey and If the remora only depends on its host for a free ride to a Lachner (1970) have suggested that it is a specialized pelagic feeding site, then the relation can be defined as commensal- species because of its large disk, reduced fins, and short ism. Blue whales charge through a patch of zooplankton, body. These modifications suggest that it is better adapted to drop their lower jaw, and engulf not only the zooplankton remain attached to a host than to free-swim. Perhaps, then, but up to 70 tons of water. The mouth is then closed and the whale-sucker may have a strong, single host preference the ventral furrows expand allowing the animals and water for cetaceans because its morphology enables it to remain on to be contained within this swollen pouch. Once the zoo- a whale through much (if not all) of its life cycle. plankton are trapped inside, the blue whale can then strain Although scattered published reports indicate that whale- out the water and swallow the prey. Presumably the remora suckers have been found on a variety of cetaceans, they are can also be actively predating on plankton at this time by most often seen attached to blue whales. Rice and Caldwell leaving the whale and pursuing the prey, or by maintaining ( 1961 ) suggest that whale-suckers may prefer blue whales to contact with the host while feeding on plankton which pass other species of cetaceans as hosts. Observations of single across the whale's body. remoras on cetaceans which are not blue whales may only be Studies by Strasburg ( 1962) of a captive shark-sucker, temporary associations. Since a whale-sucker is not well Remora remora, suggest that the remora's need to maintain its adapted to free-swim, it may tolerate a short-term attach- attachment to a host can interrupt its feeding. Strasburg ment site on any large, moving object when in the absence of found that as the host-to-prey distance increased, the prob- the more preferred blue whale host. For example, a remora ability decreased that the remora would leave its attachment would occasionally attach itself to our boat until we site to predate on food particles. Further studies show that a approached a whale, whereupon it would invariably disen- remora can recognize an individual attachment site a gage itself and reattach to a whale-host. immediately reattach after retrieving a single particle food. (It did not leave the host to forage for extended peri- ods of time.) Strasburg also found that remoras can slide forwards backward, or ideways (as if in a semi-attached manner) when pursuin prey close to the body of the host. Based on the feeding behavior of this species, one can specu- late that a blue whale, w is traveling rapidly through a school of plankton, might leave behind a remora which detaches itself. It is likely, then, that a remora will choose to maintain close contact with a feeding whale until the whale has slowed or stopped to filter its huge mouthful of water. At this time the remora could more safely leave the whale to predate on the crustaceans which escape from the whale's mouth. Cressey and Lachner found that suckerfish do not exclu- sively feed on or around their host, but also inside their host's mouth. Although most of these observations were not based on the habits of a whale-sucker and its host, F.T. Bul- A. Represents ventral view of fish on "our" side of whale len noted in 1904: B. Represents dorsal (top) view of fish "through" to other The suckers delighted quarters in the mouth of a right side of whale whale, adhering to the palate with its head pointed in C. Represents profile of fish stuck onto underside of whale the direction from whence the whale's food enters so that it easily receives tithe of all without the slightest effort in its part to obtain it. Since right whales feed on copepods, euphausiids, and pteropods, it is possible that this account was accurate and the remora was consuming crustaceans which entered the whale's mouth. If a remora chooses to enter the mouth of a whale, then it must be able to migrate freely along the surface of its host \ without loosing its attachment site. Mahnken and Gilmore Sucker Plate (1960) watched a remora traverse from the left to the right side of a spotted dolphin, while the animal was moving at about 10 knots off the bow of a boat. Why would a remora want to wander around an animal if it only wanted a ride to a feeding site? Certainly it would seem more expedient for a remora to lie stationary, expend less energy and decrease its chances of falling off while hanging-on to the dolphin at this speed. The fact that a whale-sucker can travel around a mov- ing animal, possibly entering its mouth at will, suggests that Figure I. Whale-Suckers (Remilegia australis) it may be a cleaner fish, capable of exploring its host in Artist's rendition from research material available. search of parasitic crustaceans. The stomach contents of six different species of remora (not including a whale-sucker) which were analyzed by Cressey and Lachner contained plankton or copepods along If the remora prefers to feed on zooplankton, then pre- with unidentified food. Seventy percent of the diet of a sumably it depends on the feeding behavior of its host to shark-sucker contained copepods which were identified as bring it to these animals. Strasburg (1962) suggested that parasites of the host species. The interaction between this because its stomach is quite small a remora probably eats remora and its host is therefore not an example of com- frequent small meals rather than occasional large ones. mensalism, but of mutualism, an interaction between two Hence, it may behoove a remora to maintain an ability to organisms where both benefit. e importance of parasitic switch prey species and take parasites from the host if its copepods in the diet of these six remora species apparently feeding requirements do not coincide with that of its host. changes during the course of the remora's development. The Chitinous material was found in the stomach of a whale- degree to which parasites are eaten varies with the size and sucker which was taken from a blue whale off California. species of remora: some are active parasite predators when Rice and Caldwell(1963) analyzed the stomach contents, juveniles; others become active with maturity. Although the but they could not identify of what animal(§ whale-sucker was not studied, it does not seem unreasonable remains were a component. Since crustaceans that this species may also act, at some point in its life cycle, characteristic chitin exoskeleton and chitinous join as a cleaner fish to cetaceans. appendages, I question if some of the rema been pieces of a copepod or amphipod. Bo mals are crustaceans which have been foun of blue whales and if the whale-sucker is a might predate on the animals. The amphipod, or whale-louse Cyantidoe balaenopterae, is a host-specific parasite of the blue whale. Rowntree (1983) has suggested that these amphipods inhabit folds of skin, wounds, or orifices on the external surface of cetaceans for protection. She also found that these animals feed on the skin of a whale and cling to it with hooked claws, which apparently may be harmful to the whale because these claws pierce the skin. In all species of remora, the lower jaw pro- jects beyond the upper jaw which could make it possible for the remora to scoop under the flattened whale lice and remove it from the whale's skin without loosing its own attachment site, thus benefiting its host by removing these parasitic lice. Blue whales also have several species of copepods inhabit* ing their skin and baleen plates, as well as a film of algae that covers their ventral surface. Since zooplankton may be patchy and unpredictable sources of food, the remora could utilize these communities of crustaceans or algae as a secon- dary food source. Other remora species have shown an affinity for their host's bucco-pharyngeal regions, which has been associated with the high concentration of parasites present in these areas. Szidat and Nani (195 1) have sug- gested that the remoras enter these regions to feed on the parasites. Consequently, if remoras inhabit the whale's mouth, there is a possibility that they too could be feeding on copepods by cleaning the baleen plates of these parasites. Whale skin was also found in the stomach of the whale- sucker that Rice and Caldwell analyzed which suggests that a remora may feed on Scraps would include not only sloughed-off whale epidermis, but the feces of the whale, as well as bits of zooplankton which escape through the baleen. Blue whale feces, which we collected, contain particles of zooplankton that Edward Brinton has tentatively analyzed as a Myscidacean. Presumably a remora could leave the whale to feed on the rapidly dispersing fecal material, or the sloughed-off epidermal tissue without necessarily loosing its host. However, blue whales off Sri Lanka were only seen defecating before dives or during rapid movement and no remoras were seen feeding on the feces. Finally, the remora may need a host for the following functional reasons: 1. The apparent need for a whale-sucker to associate with one whale species, the blue whale, in large aggregations may be linked to its reproductive restrictions. If both sexes do not attach to the same individual, or if a whale-sucker attaches to any large, plankton-feeding animal, then the chances of spawning might be limited. As Strasburg (1964) has suggested, mating could only occur by chance or when the individuals of the host species aggregated to feed, to mate, or to migrate. Do both sexes attach to one individual in order to mate or does spawning occur elsewhere? Cressey and Lachner observed that remora "families" composed of immature and mature males and females inhabit the same individual whale, which strongly suggests

A blue whale (Balaenoptera musculus spp.) off the East Coast of Sri Lank with one to two remoras attach

Whalewatcher Spring 1985 that mating may occur on the host. is would enable the remora species to reproduce independently of the social behavior of the host species. 2. Although there is no substantial evidence that cetaceans afford protection for remoras, a free-swimming remora s removed, then the interaction would probably be more vulnerable to predation than one seems to be more substantive that is attached to a whale. Cressey and Lachner suggested that juveniles may attach themselves to the palate of their host, not only to avoid competition with adults who are for respiration, as a resource for food, and for transporta- feeding on the surface of the body but also for protection. tion. The host may also act as a refuge for the remora to 3. Currents derived from the movement of a whale could escape predato as a site for successful reproductive aid in the remora's respiration by decreasing the expenditure opportunities. of energy required for opercular breathing movements. In a laboratory study, Strasburg (1957) showed that a jet of water aimed at the mouth of a shark-sucker increased the study was funded by the World availability of dissolved oxygen to the gills. When in quiet Fund. I thank Dr. E. Brinton of the University of California water, a great expenditure of energy is required for the for analyzing the blue whale feces and the personnel at the remora to respire, while an optimal flow of water past the Center for Long Term Research for their assistance while animal ceases all opercular movements. using their facilities. I am especially grateful to Roger Payne Since a small animal has a larger surface/volume ratio and Jonathan Gordon for their comments and suggestions. than a large animal, one might expect that its ability to References are available upon request. respire requires less energy. It is possible, then, that a young remora could inhabit the mouth of a whale without having Abigail Ailing is a Doctoral Candidate at the School of Forestry to depend on the movement of water through its gills for and Environmental Studies, Yale University. (Photos by Abigail respiration. Alling, courtesy of the World WiIdlife Fund International)

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