Lethrinops chilingali, Turner & Crampton & Genner, 2023, Turner & Crampton & Genner, 2023

Turner, George F., Crampton, Denise A. & Genner, Martin J., 2023, A new species of Lethrinops (Cichliformes: Cichlidae) from a Lake Malawi satellite lake, believed to be extinct in the wild, Zootaxa 5318 (4), pp. 515-530 : 527-528

Relationship of L. chilingali to other taxa in the Lake Malawi radiation

The present study has assumed that L. lethrinus is both the most likely sister taxon for L. chilingali and the species most likely to interbreed with it, should habitat barriers be broken down. The former proposition is based on their overall similar appearance, including very similar male breeding dress, and similar – although distinct- melanin patterns in the females and juveniles. They are the only two known Lethrinops species to share a largely horizontally-banded melanin pattern. Other Lake Malawi cichlids also share some of these features, notably species of Protomelas Eccles & Trewavas 1989 found in similar shallow weedy/muddy habitats, including Protomelas kirkii ( Günther 1894) , Protomelas similis ( Regan 1922) and Protomelas labridens ( Trewavas 1935) ( Eccles & Trewavas 1989, Konings 2016, Turner 1996). These three species also have females/immatures with a sandy/countershaded appearance, with a strong horizontal dark band running along the flank. Males are also metallic blue-green, with a red and white dorsal fin margin. These species have shorter snouts and more upwardly-angled mouths than L. lethrinus , but so does L. chilingali , which is arguably morphologically intermediate between them. The genera Protomelas and Lethrinops can be distinguished by the shape of the lower jaw dental arcade, and it is presently assumed that this is a phylogenetically informative trait ( Eccles & Trewavas 1989), although this requires confirmation from a phylogenetic analysis, ideally based on genome-scale sequence data. A published phylogenomic analysis places L. lethrinus in the middle of a clade of shallow water Lethrinops , Taeniolethrinops and Tramitichromis ( Masonick et al. 2022) , thus grouping these genera showing Lethrinops - type dentition ( Eccles & Trewavas 1989). However, P. kirkii , P. similis and P. labridens were not included in that analysis ( Masonick et al. 2022). Notably, however, an additional group of deep-water Lethrinops appears in a separate part of the phylogenetic tree, suggesting that the Lethrinops - type dentition is prone to parallelism. Thus, we conclude that available evidence does not conflict with L. chilingali being a sister species to L. lethrinus , but this requires detailed phylogenetic investigation for confirmation. If L. lethrinus shows relatively high levels of population structure, it could be paraphyletic (ancestral) with respect to L. chilingali .

Distributions of L. chilingali and L. lethrinus

Lethrinops chilingali has only been positively recorded from Lake Chilingali, but here we consider whether it may have a broader distribution in Lake Malawi, possibly extending to the central to northern part of the lake as an allopatric sister species to L. lethrinus . Although a lake-wide distribution has been claimed for L. lethrinus ( Konings 2016) , the great majority of records backed by preserved specimens or photographs come from the southern arms, Lake Malombe and the Shire River ( Eccles & Lewis 1978, Turner 1996, Konings 2016). On the Global Biodiversity Information Facility website ( GBIF 2023), there is a record of Lethrinops lethrinus from co-ordinates indicating a collection site off the Tanzanian shore near Ngkuyo Island, Mbamba Bay (11.334°S, 34.769°E), based on specimens at the South African Institute for Aquatic Biodiversity (SAIAB). An offshore location near a rocky headland seems an unlikely collecting site for Lethrinops lethrinus , which favours shallow sheltered vegetated habitats and the locality label is given as ‘Lifuwu’, which probably corresponds to the vicinity of Lifuwu village (13.69°S, 34.60°E) just north of Salima, suggesting that the co-ordinates have been recorded in error. The single small specimen shows no melanic markings (faded post-preservation?), but the head shape is consistent with Lethrinops lethrinus rather than L. chilingali . Another GBIF record from co-ordinates 13.35°S, 33.4°E would suggest specimens were collected from the Rusa River, a tributary of the Bua River, which joins Lake Malawi near Lake Chilingali. The site is far upstream, around 97km West of the Lake Malawi shore at Benga, and initially we thought this might suggest specimens of L. chilingali could be widespread in the river catchment. However, the collection label indicates the specimens were collected from Lake Malawi at Foo, which is a trawling station in the SE Arm of Lake Malawi (also sometimes written as Fowo), which is at approximately 14.14°S, 35.18°E, again suggesting an error in the co-ordinates. Photographs of the specimens show typical Lethrinops lethrinus , with long snouts and strong horizontal melanic markings. The catalogue of the Natural History Museum in London contains a single accession of three specimens labelled as L. lethrinus from Lupembe Sand Bar, collected by Cuthbert Christy in 1925 (BMNH 1935.6.14.2077-9; Figure 4 ). The electronic catalogue suggests that this location is in Tanzania, perhaps following Eccles & Trewavas (1989) who suggested it might represent a site at the mouth of the ‘Kivira River’. However, the town at the mouth of the Kiwira River (as presently named) is currently known as Itungi Port. It is more likely that the 1925 collection site is Lupembe on the Malawian lakeshore, just south of Karonga (10.055°S, 33.99°E). Notably, recent satellite images show a conspicuous sandbar (Google Earth). Examination of the unpublished diary of Cuthbert Christy held at the Natural History Museum shows a single accession from Lupembe following an extensive collection of several hundred accessions from Vua / Deep Bay (Chilumba area) and immediately before another extensive collection from Mwaya in Tanzania, on the far north coast of the lake (itemising various river mouths visited). No other accessions were made from Lupembe. This suggests that the location was visited en-route from Chilumba to Tanzania, which would fit well with the location near Karonga. Unfortunately, the specimens (fig. 5a) are very small (44.8–50.9 mm SL) which makes morphological comparisons difficult with the larger specimens examined for this study, due to allometric effects. For example, they have notably relatively large eyes, making snout measurements relatively small. However, the low position of the mouth on the head and the largely continuous midlateral stripe, fit far better with L. lethrinus than with L. chilingali . Thus, available museum specimens strongly support the occurrence of typical Lethrinops lethrinus only in the southern arms of the lake, but tentatively indicate that they may also occur just north of Senga Bay and indeed almost at the northernmost extremity of the lake, but do not provide evidence for the occurrence of L. chilingali or any other similar form within Lake Malawi,

Other published records are not backed by specimens available to examine or photographic evidence. Eccles & Lewis (1978) reported that they had found L. lethrinus at Nkhata Bay, which is well to the north of Lake Chilingali. However, they reported an unusual melanin pattern: “the dark line along the middle of the flank curves upwards anteriorly to merge with the lower of the two rows of spots and the spots themselves may run together posteriorly to form a stripe”. The occurrence of specimens with dramatically different stripe patterns at Nkhata Bay might lend credence to the idea that L. lethrinus represents a complex of allopatric taxa, which might increase the probability that L. chilingali might persist in the main Lake Malawi. Eccles & Lewis provided no illustration of this ‘ Nkhata Bay variant’. Their specimens were deposited in the collection of the Monkey Bay Fisheries Research Unit, Malawi and their present status is unknown. The pattern described is reminiscent of that seen on some of the type specimens of L. leptodon Regan 1922 (fig. 5b). In the same 1978 paper, Eccles & Lewis redescribed that species based on a single specimen collected from Chintheche in the NW of the lake, near Nkhata Bay, but their illustration of that specimen showed a clear midlateral blotch on the upper part of the flank. They reported examining, but not measuring, three of the type specimens of L. leptodon , which are held at the Natural History Museum in London (BMNH 1921.9.6.201- 207, collected by Wood from somewhere in ‘Lake Nyasa’). Thus, it seems unclear whether the reported Nkhata Bay populations represent L. lethrinus or L. leptodon , or indeed something else. In summary, the status of the northern populations of Lethrinops of this group is unclear but is consistent with the hypothesis that L. lethrinus is found in suitable habitats throughout Lake Malawi, and that L. chilingali is a satellite lake endemic extinct in the wild.

Conservation status of Lethrinops chilingali

Lake Chilingali is approximately 5km in length and a maximum of 1km in width, and is characterised by two deeper basins of approximately 5m depth separated by a shallower plateau ( Turner et al. 2019). It has a single outflow, the Kaombe River, which meanders for approximately 12km before reaching the main body of Lake Malawi ( Genner et al. 2007). The lake is a natural water body, and the two basins of the modern lake are represented on early European exploration maps, as two separate bodies of water, Lake Chikukutu to the south, and Lake Chilingali to the north ( Turner et al. 2019). The lake level was raised when a dam was constructed across the single outflow for irrigation purposes, initially in the 1950s, before being modified in the early 1970s ( Denys et al. 2013). The dam collapsed early in 2012 ( Denys et al. 2013), and the single lake disappeared, reforming the two separate smaller shallow basins. In 2016 these basins were estimated to be only ~ 1m deep and fringed with macrophytes. The lake was refilled to approximately its pre-collapse-level in June-July 2019 following the construction of a new dam.

During the period 2004 to 2011, before the collapse of the dam, L. chilingali was periodically and reliably sampled from the lake, alongside another apparently endemic haplochromine cichlid, the undescribed Rhamphochromis sp. “chilingali” ( Genner et al. 2007; Turner et al. 2019). To our knowledge, the last sampling event where L. chilingali was recorded in the wild was on 25 June 2009 (by G. Turner), while representatives of R. sp. “chilingali” were last collected from an artisanal fishing catch on 12 January 2011 (by M. Genner). During sampling in February 2016, neither of the species was encountered in a survey of the main northern and southern basins of Lake Chilingali ( Turner et al. 2019). A survey in April 2022 also failed to sample any either L. chilingali or R. sp “chilingali” but did find that Lake Malawi endemic Otopharynx tetrastigma ( Günther 1894) was abundant (H. Svardal, pers comm). This species was absent between 2004 and 2016 and is likely to have been introduced during restocking after the lake was refilled in 2019 (H. Svardal, pers comm). Although further surveys of Lake Chilingali and the Kaombe river are warranted to determine if remnant populations of either L. chilingali or R. sp “chilingali” persist, on the basis of the current evidence, we consider it most likely that both species are no longer present in the natural environment. Breeding populations of L. chilingali or R. sp “chilingali” are, however, maintained in captivity, and may be candidates for reintroduction. On the basis of the evidence discussed above, we recommend that L. chilingali is attributed the status of Extinct in the Wild (EW) on the International Union for Conservation of Nature (IUCN) Red List of Threatened Species.

Figures

FIGURE 4. a. Lower pharyngeal bones of Lethrinops lethrinus, 128mm SL, BMNH 2023.1.11.49-50 (left); Lethrinops lethrinus 84mm SL (unregistered, bottom right); Lethrinops chilingali 69mmSL (unregistered, top right); b. Distribution of Lethrinops lethrinus specimens examined (●), unconfirmed records: juveniles or not examined (Q) and Lethrinops chilingali (●).