Review of marine fish zoogeography of Chilean Patagonia ( 42 °-57 ° S ) *

The ichthyofauna of the West Patagonian Region (42oS-57oS) is composed of a conjugation of diverse faunistic elements such as: endemic species of the sector, low latitude species, Atlantic species, Antarctic species and oceanic circumglobal species. The colonization of the Patagonian coast by recent fishes has been estimated to have started about 20,000 years ago, when gradually and with the development of the Southern channel system and especially the Straits of Magellan, an increasing mixture among the Pacific and Atlantic communities took place (Lloris and Rucabado, 1991). This process began after the last ice-age, whose maximum intensity was about 27,000-18,000 years BP, and during which the glaciers totally covered the actual Patagonian territory (Pisano, 1975). SCI. MAR., 63 (Supl. 1): 451-463 SCIENTIA MARINA 1999


INTRODUCTION
The ichthyofauna of the West Patagonian Region (42ºS-57ºS) is composed of a conjugation of diverse faunistic elements such as: endemic species of the sector, low latitude species, Atlantic species, Antarctic species and oceanic circumglobal species.The colonization of the Patagonian coast by recent fishes has been estimated to have started about 20,000 years ago, when gradually and with the development of the Southern channel system and especially the Straits of Magellan, an increasing mixture among the Pacific and Atlantic communities took place (Lloris and Rucabado, 1991).This process began after the last ice-age, whose maximum intensity was about 27,000-18,000 years BP, and during which the glaciers totally covered the actual Patagonian territory (Pisano, 1975).
In the present revision, information on bathymetric and latitudinal distribution of marine fishes known for western Patagonia is gathered from the literature, personal collection and observations.Venegas and Sielfeld (1998) presented part of these data for the fishes of Magallanes and the Antarctic, and Sielfeld and Vargas (1992) for Chilean sharks and rays.These data are analyzed and compared with results of previous biogeographic studies of the area.In the future they may help to plan, in a more direct manner, further ichthyological research in this region.
The latitudinal and bathymetric analyses were mainly based on the bibliographical information (see Table 1).Additionally, information obtained by personal observations by the authors in the area is also included.
The list of species in Table 1 does not include Pseudomancopsetta andriashevi Evseenko, 1984, only known very far off the south Chilean coast (Heemstra, 1990).Aplochiton marinus Eigenmann,1928 is maintained as a valid species following Zama and Cárdenas (1984), although its conspecificity with A. taeniatus Jenyns, 1842 is suspected(see Mc Dowall, 1971b).Lycodapus australis Norman, 1937 is excluded from the analysis because of its uncertain status.Bathyraja griseocauda (Norman, 1937), Raja doellojuradoi Pozzi, 1935 and Raja frerichsi Krefft, 1968 are excluded from the analysis, despite their presence off the Pacific and Atlantic coasts (Pequeño and Lamilla, 1993), because their occurrence has not yet been documented for the South Chilean Patagonian coast.Patagonotothen ramsayi (Regan, 1913) and P. wiltoni (Regan, 1913) are maintained as valid species according to Stehmann and Balushkin (1993).Harpagifer palliolatus Richardson, 1845, cited by Lloris and Rucabado (1991) for the Beagle Channel, is maintained as subspecies of H. bispinnis Schneider, 1801, as indicated by Nybelin (1947Nybelin ( , 1969) ) and Lloris et al. (1996).The species of Agnatha were excluded, because the existent information was considered insufficient by authors, to support the present distributional analysis.Scymnodon macracanthus Regan, 1906 is only known by its holotype from the Straits of Magellan (Compagno, 1984).It was excluded from the analyses.Paralabrax humeralis (Valenciennes, 1828), reported for Smyth Channel, Punta Arenas, by Lönnberg (1907), needs to be confirmed for the region, because of the thermophilous character of the fishes of this family.Notorhynchus cepedianus (Peron, 1907) was reported by Guzmán and Campodónico (1976) for the eastern entrance of the Straits of Magellan.As this genus is wideranging in temperate seas, distributed from Peru to central Chile in the South Eastern Pacific (Compagno, 1984), the Magellan specimens are here considered as belonging to the Atlantic population.
In the analysis of the latitudinal distribution, the eastern sector of the Straits of Magellan (east of 71ºW) was excluded, this area being treated separately.The cluster analyses were expressed in form of dendrograms using Jaccard's qualitative index of similarity (Sj).The applied aggregative algorithm was the UPGMA method which uses arithmetic means (Menni and Gosztonyi, 1982;Sielfeld et al., 1995;Sielfeld and Vargas, 1996), with the following equation: where: a = number of species endemic to group A b = number of species endemic to group B c = number of species that are in group A and B

Bathymetric analysis
The bathymetric analysis for 95 species of marine fishes of the extreme south of Chile (42º-57ºS) showed the existence of three fish associations (over 30% of similarity) (Figure 2).One of them groups fishes distributed between 0 and 50 m depth, clearly separated from the remaining associations (similarity less than 10%).59 species integrate this group, 36 of them (61%) endemic (Table 2 ) and belonging to families like Triakidae, Galaxidae, Aplochitonidae, Gobiesocidae, Syngnathidae, Atherinidae, Agonidae, Normanichthyidae, Pingui- Halargyreus johsoni Günther, 1862 A second group, below 50 m and down to 500 m, is formed by 56 species, 24 (43%) of which are endemic species of the families Ophidiidae, Carapodidae, Cottunculidae and Scopthalmidae.
A third group, from below 500 m of depth, presents 20 species, has no endemic families, and only Etmopterus granulosus and Coryphaenoides filicaudus are endemic species.This species group segregates as independent group in the cluster analysis, because of its species poverty, and will here be considered as part and marginal condition of the 50-500 m depth fish assemblage (see Table 2).

Latitudinal analysis
The analysis of the latitudinal distribution of the fish groups at the 0-50 and 50-500 m depth level, show four ichthyogeographical sectors: a "northern sector" (42º to 46-47ºS), an "intermediate sector" (47-48º to 51ºS) and a "southern sector" (52º to 56ºS) (Figures 3 and 4).The fauna at 57ºS (Diego Ramírez Islands) appears as an independent group, characterized by its poverty of species (result of scarce sampling), although it seems to be part of the previously defined "southern sector".The fishes below the 500 m depth level show three groups with a "northern sector" of similar range as the groups before(42º to 46ºS), and an "intermediate sector" (47ºto 54ºS) and a "southern sector" that includes the fauna at 57ºS.
The "northern sector" of the 0-50 m depth level is mainly characterized by the presence of the families FISH ZOOGEOGRAPHY OF CHILEAN PATAGONIA 457 Tripterygiidae, Labrisomidae, Clinidae, Blenniidae, Pinguipedidae, Branchiostegidae, Normanichthyidae and the species Bovichthus chilensis, Hippoglossina macrops and Paralichthys microps.In the "intermediate sector", different typical families of lower latitudes find their southern distributional limit between 45º and 46ºS (Blenniidae, Clinidae and Normanichthyidae), and between 46º and 50ºS (Cheilodactylidae, Branchiostegidae and Gobiesocidae).Within the same sector the 50º-52ºS latitudes represent the northern distributional limit of the family Harpagiferidae and some species belonging to the "southern sector" such as Cottoperca gobio and Careproctus crassus.The "southern sector" corresponds to the West-Fuegian Archipelago, and its ichthyofauna is characterized by the great speciation of the families Nototheniidae (mainly belonging to the genus Patagonotothenia) and Zoarcidae (genera Austrolycus, Iluocoetes, Crossostomus, Phucocoetes, Dadyanos and Letholycus) (see Table 2).

Straits of Magellan
At least 58 species (see Table 1) are represented on both sides of Patagonia, mainly corresponding to species of the families Squalidae, Rajidae, Gadidae, Moridae, Muraenolepidae, Zoarcidae and Nototheniidae.There are insufficient data to determine how many of these species are really present in the Straits of Magellan, nevertheless the study of the actually known longitudinal distribution (68º-74ºW) of fish species along the Straits of Magellan (Table 1), shows a gradual transition from east to west (Table 3) with a westward decrease in the number of species and in the occurrence of typical Atlantic species (e.g.Paralichthys patagonicus, Austromenidia nigricans, Phucocoetes latitans, Netuma barbus) up to approximately 71ºW.(Notorhynchus cepedianus and Symnodon macracanthus may also correspond to this group).

DISCUSSION
The studied fish fauna corresponds to the" Magellan District" and to the fishes of the "Patagonian Region" as defined respectively by Regan (1913) and Norman (1937), with its northern limit in the region of Chiloé (41º30'S).
The bathymetric distribution analysis of 95 fish species distributed between the latitudes 42º-57ºS shows the existence of a group of coastal or shallow water fishes (0-50 m depth), clearly different (low similarity) to a group of deep water fishes or "fishes of the shelf" (below 50 m depth), fully corresponding with the "Subantarctic Region" and "Deep Waters" established by Nakamura et al. (1986) for the south of South America.Both species associations showed similar north-south distribution trends, with a well defined "northern sector" characterized by the dominance of low latitude elements (of the "Valdivian District", sensu Balech, 1954), a "southern sector" with endemic elements, and an intermediate "transition sector", that must be considered as an independent unit, according to its extension and ichthyological composition.This "transition zone" extends from the sector of the Taitao peninsula to the Magellan Straits.These before recognized sectors, agree, respectively, with the divisions proposed by Hart (1946) and named "North Region", "Intermediate Region" and "South Region", and the divisions of Laevastu (1961), named "Peruvian-Chilean Region", "Area of Transition" and "Patagonic Region".As has been indicated by López (1963) and Lloris and Rucabado (1991), the latitudinal zonation of the "coastal fishes" and the "fishes of the shelf" seems to bear relation with the "West Wind Current" and its division in front of the Chilean coast at 41ºS, in a northward going branch, or "Peru Current" and a southward flowing branch, or "Cape Horn Current" (Sverdrup et al., 1942).This oceanographic situation apparently acts as a northern dispersion barrier, along the Pacific Patagonian coast, for more southerly faunistic elements, and may explain the separation of the "Valdivian District" and the "Chiloé District" (sensu Balech, 1954).
In the particular case of the "coastal fishes" of this study, the "northern sector" and "intermediate sector" correspond very well with the before indicated "Chiloé District" of Balech (1954), despite some differences in their latitudinal extensions.Future analyses of this geographic area will probably produce important information, such as the existence of a low salinity sector of channels and sounds of estuarine character (Pickard, 1971) and an oceanic coastal sector, with similar characteristics of salinity and wave exposure, corresponding to the shores of lower latitudes in Chile.This would eventually explain the latitudinal overlap of the north distribution range of the fishes of the previous sectors and the south range of the fishes of the Valdivian District.The latter seem to be mainly distributed along the oceanic coastline.Only a situation of this type can explain the presence in the far south of the Magellan Region of Syciases sanguineus Müller and Troschel, 1843 (see Sielfeld, 1979 a) and Gobiesox marmoratus Jenyns, 1842 (pers. obs.).The previous distribution pattern also gives sense to the records of Aphos porosus (Valenciennes, 1837) and Paralabrax humeralis (Valenciennes, 1828) by Lönnberg (1907) and Pinguipes chilensis (Molina, 1782) by Lorentzen et al. (1979) for the Magellan Region.
Nevertheless, a more detailed and complete knowledge of the ichthyogeography of the Patagonian Archipelago needs to take into account other aspects, especially those related with its particular environment.The following have been identified to be of particular importance: 1. -The geological conformation of the coastline and the relationship between beach types (granulom-etry and inclination), the sea floor and the fish community: It must be noted that beaches of the Atlantic sector are of little inclination and largely formed by morrenic and aluvial materials, while those of the Pacific sector principally correspond to diorites, basalts and metamorphic rocks, determining rocky coasts of strong inclination.This geological structure is arranged parallel to the Pacific margin and the transition between the two types of shore occurs at the level of the central portion of the Straits of Magellan (Instituto Geológico de Chile, 1968).
2. -The extension of the continental shelf and its importance in the distribution and abundance of demersal fishes: The Chilean shelf broadens progressively southwards, attaining its maximum extension (50 nautical miles) to the southwest of the Cape Horn Archipelago (Ojeda, 1983), where the marine bottom is mainly constituted of sand, mussel and coral sands and Foraminifera (Nakamura et al., 1986).
3. -The effect of rainfall on the intertidal pools: A strong north-south and east-west increase of the precipitation is typical of Patagonia (Jeréz and Arancibia, 1972;Zamora and Santana, 1979), with annual variations ranging from 200 mm (eastern sector of the Straits of Magellan) to 8.500 mm on the west coast (Guarello Island).The effect on the intertidal pool communities has not been evaluated yet.
4. -The currents in the channels, produced by tidal changes, and their effect on the coastal fauna of the interior channels and their distribution is important.
5. -The Patagonic zone presents four main sea surface currents: The Cape Horn Current, Peru or Humboldt Current, Falkland Islands Current and Brazil Current (Nakamura et al., 1986); only the first two directly affect western Patagonia.The effect of these currents on the distribution of the fish has been analyzed by López (1963), although further studies and research, on a more local scale, are necessary.
6. -In addition to the previous aspects, attention should also be given to complementary details such as the effect of the degree of tide-height on litoral and intertidal fish communities, the vast continental glaciers, the snowdrifts and their effect on salinity, the composition of the bottom ichthyofauna of the deep channel sectors and sounds, and the effect of the oceanic waves on the litoral communities.
FIG. 1. -The study area and representation of the ichthyogeographic sectors found for costal and shelf fishes of Western Patagonia: I.-Approximate shelf-fish distribution; II.-Distributional area of Patagonian shallow water fishes; a.-northern sector; b.-intermediate sector; c.-southern sector.

TABLE 1 .
-Latitudinal and bathymetric distribution of the here considered species of marine fishes.Used terminology: Atl.= Atlantic; Int.= intertidal; * = personal not published information. .

TABLE 1 .
(Cont.) -Latitudinal and bathymetric distribution of the here considered species of marine fishes.Used terminology: Atl.= Atlantic; .

TABLE 2 .
-Distribution of species by sectors and bathymetric levels.Used terminology: N northern sector; I: intermediate sector; S: southern sector.

TABLE 2 .
(Cont.) -Distribution of species by sectors and bathymetric levels.Used terminology: N northern sector; I: intermediate sector; S: southern sector.