Coregonus obliterus, Selz & Seehausen, 2023

Selz, Oliver M. & Seehausen, Ole, 2023, A taxonomic revision of ten whitefish species from the lakes Lucerne, Sarnen, Sempach and Zug, Switzerland, with descriptions of seven new species (Teleostei, Coregonidae), ZooKeys 1144, pp. 95-169 : 95

Coregonus obliterus sp. nov.

Figs 11 , 14

Coregonus sp. ‘Albock’: Fatio 1885.

Coregonus sp. ‘Albeli-Albock’: Fatio 1890 (see also synonymy of C. zugensis ).

Coregonus lavaretus nat. riusensis, oekot. primigenius nanus: Steinmann 1950 (see also synonymy of C. muelleri and C. sarnensis ).

Coregonus wartmanni compactus : Fatio 1890 (see also synonymy of C. zugensis ).

Material examined.

Holotype. Historical specimen (year 1937): NMBE-1076268 (EAWAG-284-1), 281 mm SL, sex male; Switzerland: Lake Zug . Paratypes. All from Switzerland, Lake Zug: Historical specimens (years 1937, 1939): NMBE-1076268 (EAWAG-284-2, EAWAG-284-4), NMBE-1076271, NMBE-1076276, NMBE-1076906 (EAWAG-956-1, EAWAG-956-2), N = 6, 250-288 mm SL .

Diagnosis.

Coregonus obliterus is a small whitefish species with moderate pigmentation of all fins and body; elongated slender body (body depth: 22.7-26.1% SL, mean = 24.3); short mouth (length of maxilla: 17-21.7% HL, mean = 19.6); pronounced rostral plate; very large eye (eye diameter: 21.5-24.7% HL, mean = 23.2) with a subtle triangular (seldom roundish) eye socket; few and very short gill rakers (longest gill raker: 7.6-10.6% HL, mean = 8.8; total gill raker number: 21-26).

Description.

Shape: Body elongated and slender. Greatest body depth anterior of the dorsal fin. Ventral profile and dorsal profile similar and slightly arched. Dorsal and ventral profile from tip of snout to interorbital mostly straight and then slightly convex to dorsal and pelvic fin origin respectively. Head long. Snout often 40-50° angle to the body axis anterior of the eye, such that the profile from the tip of the snout to the vertical projection where the anterior part of the eye crosses the dorsal profile is straight and afterwards slightly convex. Snout moderately long and tip of snout quite deep with a strongly pronounced rostral plate. Mouth short and terminal to sub-terminal. Very large eye with a subtle sickle cell-shaped (seldom roundish) eye-socket. Pectoral fin short and tapered. Caudal peduncle moderately stout. Meristics: Few and very short gill rakers. Colour: Pigmentation of fins and body moderate in preserved specimens. All fins moderately pigmented at the median to distal parts of the fin. Operculum with one black spot on the lower margin of the pre-operculum. Preserved specimens are brownish in colouration.

Differential diagnosis.

The differential diagnoses against the historical specimens of C. supersum and C. zugensis from Lake Zug are given under those species’ accounts.

Distribution and notes on biology.

Coregonus obliterus occurred in Lake Zug and is extinct today (this is discussed in more detail in the Suppl. material 1: paragraph 4). Fatio (1885) mentions three whitefish species for lake Zug, ‘Balchen’, ‘Albock’, and ‘Albeli’, but later Fatio (1890) only mentions two whitefish species for Lake Zug, namely the ‘Balchen’ ( Coregonus schinzii helveticus var. zugensis ) and the ‘Albeli-Albock’ ( Coregonus wartmanni compactus ). Interestingly, Wagler (1937) noted two species to be present in Lake Zug with a remark that a third species may exist, but that it’s status is uncertain. Fatio (1890) does mention that fishermen have suggested that among the ‘Albeli-Albock’ there are individuals that are smaller and spawn later in the year, which they refer to as ‘Albeli’, when compared to the individuals they refer to as ‘Albock’ that are slightly larger and spawn earlier in the year. However, the specimens that Fatio (1890) could examine did not warrant this distinction and thus he suggested to group the two entities under the name ‘Albeli-Albock’. Fatio (1890) suggest the the ‘Albeli-Albock’ spawn in mid-September to mid-October in Lake Zug at depths of 150-180 metres. In the table Fatio (1885: table 1) states that the ‘Albeli’, C. zugensis , spawns in the deeper parts of the lake ( ‘fond’ in French) and that the ‘Albock’, C. obliterus , spawns in even deeper waters of the lake ('grand fond’ in French). Based on the findings that Lake Zug did harbour three species of whitefish and taking into account the spawning table and notes referring to the table in Fatio (1885) and the reports by local fishermen from that time period ( Fatio 1885, 1890) we suggest that this spawning period and depth should be accounted for ‘Albock’, C. obliterus . It seems based on the phenotype of C. obliterus including the spawning time and depth and the few and short gill rakers of this species, that this species must have occupied a similar ecological niche as is known for two whitefish species from two other lakes in Switzerland. C. gutturosus (today extinct) from Lake Constance and C. profundus from Lake Thun share many ecological and morphological characters with C. obliterus . More is known about the biology of these two species; C. gutturosus was (extinct today) and C. profundus is a profundal specialist feeding predominantly on benthic prey items and living and spawning in great water depths.

Etymology.

The name in Latin obliterus means 'erased from memory’ or ‘forgotten’. The name highlights that this species was forgotten for more than a century in the scientific literature. An adjective.

Common name.

We suggest the German name Zugeralbock.

Figures

Figure 11. Coregonus obliterus, Lake Zug, Switzerland A holotype, NMBE- 1076268, 281 mm SL, male, preserved specimen B paratype, NMBE- 1076268, 276 mm SL, female, preserved specimen. Scale bars: 1 cm.

Figure 14. Illustrations of specimens of each species of Coregonus from Lake Lucerne and Sarnen. Illustrations of Lake Lucerne species are based on several individuals. Illustration of C. sarnensis is based on NMBE- 1078159, 230 mm, male. Scale bar for C. sarnensis: 1 cm.