Pumpkinseed established in 12 Cyprus Natura 2000 sites, survey finds

A field study of 21 Natura 2000 sites and nearby freshwater habitats in Cyprus found the invasive North American pumpkinseed, Lepomis gibbosus , in 12 protected areas surveyed between November 2022 and November 2023. The fish occurred in 15 of 22 reservoirs and lakes but in only four of 26 sampled rivers, indicating that its distribution was concentrated in standing waters rather than river channels. Analysis of 68 fish showed an invertebrate-heavy diet, with chironomid larvae, molluscs and crustaceans forming its principal food sources.

The sampling area encompassed 19 river catchments, 21 reservoirs, Paralimni lake and 67 watercourses with a combined length of 799 km. Of those waterways, 182 km had perennial flow and 617 km had temporary flow, including ephemeral and intermittently dry channels. Arid sites drained only by temporary watercourses were excluded, so the findings do not constitute a complete island-wide inventory.

Pumpkinseed was recorded in 15 of the 22 surveyed reservoirs and lakes, producing a total catch of 429 fish. It was relatively abundant in the Evretou, Arminou and Germasogeia reservoirs, while catches were negligible in Kouris, Dipotamos, Kannaviou and Agia Marina. Pumpkinseed and largemouth bass were among the most frequently occurring members of the reservoir fish communities, and the two species co-occurred in 86.6 percent of the surveyed reservoirs.

This association prompted the authors to suggest that pumpkinseed may sometimes have entered Cyprus with bass introduced for angling, although the field data did not directly establish how the species arrived. Occurrence in rivers was much less widespread. Pumpkinseed was found in the Diarizos, Maroullena, Akaki and Syrkatis rivers, representing four rivers, or 15.4 percent of the 26 watercourses selected for sampling.

It appeared at only 6.6 percent of river sampling sites, including locations immediately upstream or downstream of reservoirs. One individual was collected from the perennial Diarizos, six from the Maroullena upstream of the Klirou-Malounta-Akaki reservoir, one from the Akaki downstream of that reservoir, and three from the Syrkatis, which feeds the Dipotamos reservoir. The distribution is consistent with limited dispersal from reservoirs during overflow, but the observations do not by themselves measure the frequency or direction of movement.

Electrofishing proved more effective than netting for detecting pumpkinseed, accounting for more than 90 percent of the total catch and confirming the species in six of the ten reservoirs sampled with both methods. Among 342 fish with recorded lengths, mean fork length was 75 mm, with a standard error of 2 mm and a range of 20–197 mm. Most, or 75.1 percent, were shorter than 100 mm, while 11 fish, or 3.2 percent, exceeded 150 mm.

Small pumpkinseed tended to concentrate near banks where vegetation or rocky substrates provided cover, whereas larger individuals occurred in the water column. The authors considered predation by largemouth bass, pikeperch and channel catfish as one possible explanation for the scarcity of large pumpkinseed, but they also noted that early sexual maturity could contribute to the pattern. For the diet analysis, researchers selected 68 pumpkinseed from reservoirs, including individuals between 80 and 197 mm in total length; their mean length was 126 mm, with a standard error of 4 mm.

They excluded fish shorter than 77.5 mm because juveniles were expected to feed almost exclusively on zooplankton. Laboratory examination produced 91 combined stomach and intestinal samples, and 22.2 percent of the analyzed apparatuses were empty. No food item differed significantly in frequency between the stomach and intestine, so the two organs were combined for the overall diet assessment.

Prey volume was estimated from material as ingested and expressed as frequency of occurrence, relative frequency, volume per item containing it and mean volume across all samples. Chironomid larvae, molluscs and crustaceans accounted for approximately 58 percent of the diet by mean estimated volume. Chironomids contributed 37.0 percent, molluscs 11.3 percent and crustaceans 11.4 percent.

The remaining diet included dipteran larvae other than chironomids, odonate larvae, terrestrial insects, fish, algae, undetermined invertebrates and several smaller taxonomic groups. Red swamp crayfish alone contributed 8.4 percent of mean volume. Fish represented 6.2 percent of the overall diet, with identifiable remains including common roach, eastern mosquitofish and pumpkinseed itself.

No evidence of predation on reptiles or amphibians was detected, but the analysis did not test for every form of impact on native aquatic vertebrates. Diet composition varied significantly among three pumpkinseed size classes, with 12 fish measuring 80–100 mm, 44 measuring 101–150 mm and 11 measuring 151–200 mm. A permutational multivariate analysis of variance found that size class explained 11.9 percent of the variation in diet composition, and a dispersion test did not detect significant differences in multivariate spread.

The principal contrasts involved molluscs, terrestrial invertebrates and dipteran larvae. Terrestrial invertebrates were absent from the 12 smallest fish, occurred in 24.3 percent of the middle size class and appeared in 56.0 percent of the largest class. Ants followed the same general pattern, reaching 32 percent occurrence among the largest fish.

The estimated terrestrial contribution of about 15 percent therefore applied to large pumpkinseed, not to the entire sample. The findings do not support treating pumpkinseed as a major direct predator of the aquatic vertebrates examined, but they also do not establish that its wider ecological effects are negligible. The survey identified several other non-native predatory fish across the reservoirs, including largemouth bass, channel catfish and pikeperch, whose diets and potential effects require separate assessment.

The critically endangered Cyprus grass snake, Natrix natrix cypriaca , has a range of about 70 square kilometres that overlaps three surveyed water bodies: Xyliatos, Aftelotos and Paralimni. Non-native predators may have contributed to the snake’s decline or hindered its recovery, but the present study did not test that causal relationship. The pumpkinseed results instead provide a baseline for future monitoring of a fish already included on the European Union list of invasive alien species of Union concern.

Because pumpkinseed was uncommon in rivers and largely restricted to reservoirs within the study area, the authors proposed prevention of new introductions as a more practical response than broad eradication. Eradication from interconnected, heavily used reservoirs would be difficult and could carry substantial social and economic costs. Regular electrofishing or environmental DNA analysis could improve detection in suitable areas.

The authors also proposed a network of ponds of different sizes, disconnected from the hydrographic system, as potential habitat for vulnerable native aquatic species because such barriers would restrict the movement of non-native fish.

Subject of Research: Distribution and feeding ecology of invasive pumpkinseed in sampled Natura 2000 freshwater habitats in Cyprus

Article Title: Distribution and dietary habits of Lepomis gibbosus in Natura 2000 sites of Cyprus

Article References: Papatheodoulou, A., Dell’Orso, M., Boz, B., Spairani, M., Zacharia, M., Tremolada, P., & Balestrieri, A. (2025). Distribution and dietary habits of Lepomis gibbosus in Natura 2000 sites of Cyprus. Nature Conservation, 59, 139-156. https://doi.org/10.3897/natureconservation.59.149036

Image Credits: AI Generated

DOI: 10.3897/natureconservation.59.149036

Keywords: pumpkinseed, Lepomis gibbosus, Cyprus, Natura 2000, invasive fish, freshwater biodiversity, dietary ecology, aquatic invertebrates, nature conservation, field survey, Distribution, dietary