Apo Island Research Articles

In-water photo-ID to estimate foraging movements of green turtles Chelonia mydas in Apo Island, Negros Oriental, Philippines

Green turtles Chelonia mydas aggregate on the western coastline of Apo Island, Negros, central Philippines foraging mainly on two species of red algae: Hypnea sp. and Gracilaria sp. We identified turtles in the foraging aggregation by photographic identification (photo-ID) of the facial scutes. Studies have shown that the facial scute patterns of sea turtles are individually unique and remain unchanged for at least a decade confirming the validity of Photo-ID as a viable method of identifying marine turtles in the wild. In-water photo-ID surveys from the end of February to the beginning of March 2018–2020 were made by taking photos of the right side of the head of each turtle. We examined 3050 clear photos of the head scute patterns resulting in identification of 129 unique individuals. Fourteen turtles were identified for three consecutive years and eight individuals identified in 2020 were also found in a 2013 poster of a green turtle photo collage taken by a dive instructor residing on the island, suggesting strong site fidelity of green turtles in Apo Island. Out of the 56 turtles identified in 2020, 42 were adults comprising 40 females (95%) and 2 males (5%). This study adds to the existing literature on the effectiveness of photo-ID in identifying turtles to evaluate foraging movements and highlights the importance of Apo Island as a foraging and developmental habitat for green turtles in the Sulu Sea region of the Philippines.

Apo Island and Sumilon Island Marine Reserves and Beyond

As a response to the destruction of coral reef ecosystems, parts of the islands of Sumilon and Apo in Central Visayas were set up as No-Take Marine Reserves (NTMR) as a strategy of conservation for coral reef and associated marine systems by the Biology Department of Silliman University in 1974. Sumilon NTMR was managed by the University for 10 years (1974–1984) and Apo NTMR for 12 years (1982–1994). Beginning from 1983 to the present, Professor Garry R. Russ of James Cook University became Silliman’s collaborator. The two coral reef systems were monitored following the methodology in the Australia-ASEAN Project manual and the genetic parentage analysis. In our work on these two reserves, we obtained the cooperation local communities in the process of setting them up. The results of the nearly annual monitoring of these two NTMRs showed that over the years the fish biomass in the NTMRs increased and fish yields of fishers likewise increased over the years. There was also evidence that there was spillover of large sized fish and fish larvae from the NTMRs to other marine areas outside the protected areas. This movement is due to ocean currents in the study areas. The results of our experiments have been published in scientific journals showing the effectiveness of the marine reserve strategy. We have influenced many people throughout the country to set up more marine reserves in addition to our work in other parts of the Visayas and northern Mindanao.

Targeted Isolation of a Cytotoxic Cyclic Hexadepsipeptide from the Mesophotic Zone Sponge-Associated Fungus Cymostachys sp. NBUF082.

LC-MS/MS-based molecular networking facilitated the targeted isolation of a new cyclic hexadepsipeptide, cymodepsipeptide (1), and two known analogues, RF–2691A (2) and RF–2691B (3), from the fungus Cymostachys sp. NBUF082 that was derived from a mesophotic zone Aaptos sponge collected near Apo Island. The constitution and configuration of 1 was elucidated through 1D and 2D NMR-spectroscopy, high resolution mass-spectrometry, and chemical degradations including Marfey’s analysis and chiral HPLC. It was observed that 1 was moderately cytotoxic against CCRF-CEM human acute lymphocytic leukemia cells in vitro with the IC50 value of 9.2 ± 1.1 μM.

Development of reproductive potential in protogynous coral reef fishes within Philippine no-take marine reserves.

Empirical evidence for increases in the reproductive potential (egg output per unit area) of coral reef fish in no-take marine reserves (NTMRs) is sparse. Here, we inferred the development of reproductive potential in two species of protogynous reef fishes, Chlorurus bleekeri (Labridae: Scarinae) and Cephalopholis argus (Epinephelidae), inside and outside of Philippine NTMRs. We estimated key reproductive parameters and applied these to species-specific density and length data from 17 NTMRs (durations of protection 0-11 years) and paired fished sites (controls) in a space-for-time substitution approach. For C. argus, we also used density and length data collected almost annually over 29 years from a NTMR and an adjacent control at Apo Island. The results suggest that C. bleekeri can develop 6.0 times greater reproductive potential in NTMRs than controls after 11 years of protection, equivalent to approximately 582,000 more eggs produced 500 m-2 inside NTMRs. Enhancement of reproductive potential in C. argus was not evident after 11 years in the space-for-time substitution. At Apo Island NTMR, reproductive potential of C. argus increased approximately 6-fold over 29 years but NTMR/control ratios in reproductive potential decreased through time (from 3.2 to 2.4), probably due to spillover of C. argus from the NTMR to the control. C. argus was estimated to produce approximately 113,000 more eggs 500 m-2 inside Apo Island NTMR at the 29th year of protection. Ratios of reproductive potential between NTMR and controls in C. bleekeri and C. argus were often greater than corresponding ratios in density or biomass. The study underscores the importance of species-specific reproductive life history traits that drive variation in the development of larval fish subsidies that originate from NTMRs.

Shore-fish assemblage structure in the central Philippines from shallow coral reefs to the mesophotic zone

Connectivity between shallow coral reefs and adjacent deeper habitats may be crucial to reef ecosystem stability. However, deeper habitats such as mesophotic coral ecosystems (MCEs) remain understudied. We investigated the depth structuring of shore-fish assemblages in the central Philippines across shallow (10-30 m) and mesophotic (upper: 30-60 m, lower: 60-90 m) depth zones. Baited video surveys in two coastal sites similar to 30 km apart showed strong declines with depth in fish species richness and abundance including fishery target species. Corallivores, herbivores/detritivores, omnivores and planktivores showed the strongest declines. Invertivores and generalist carnivores dominated abundance at mesophotic depths. Data from the coastal sites were analysed with published data from an offshore island (Apo Island) < 25 km away to provide broader insights on spatial variability of shore-fish depth structuring. The percentages of species that overlapped shallow and mesophotic depths were much lower in coastal sites (9-13%, 9-11%) than the island (20-26%), suggesting higher potential vertical connectivity in the latter. Mean assemblage similarities (Bray-Curtis) between shallow and mesophotic depth zones were found to be low at all sites (0.3-19.6) and decreased with depth. Fish assemblages gradually differed across depth zones at coastal sites but mesophotic assemblages at the island were more similar to the shallow coastal assemblages. Strong correlations between fish assemblages and benthic habitat were detected, suggesting that higher cover of rocky substratum at mesophotic depths facilitates vertical connectivity at the island. Our findings highlight benthic habitat as a driver of spatial variation in the depth structuring and vertical connectivity of shore-fish assemblages.

Partitioning no-take marine reserve (NTMR) and benthic habitat effects on density of small and large-bodied tropical wrasses.

No-take marine reserves (NTMRs) are increasingly implemented for fisheries management and biodiversity conservation. Yet, assessing NTMR effectiveness depends on partitioning the effects of NTMR protection and benthic habitat on protected species. Such partitioning is often difficult, since most studies lack well-designed sampling programs (i.e. Before-After-Control-Impact-Pair designs) spanning long-term time scales. Spanning 31 years, this study quantifies the effects of NTMR protection and changes to benthic habitat on the density of tropical wrasses (F. Labridae) at Sumilon and Apo Islands, Philippines. Five species of wrasse were studied: two species of large-bodied (40–50 cm TL) Hemigymnus that were vulnerable to fishing, and three species of small-bodied (10–25 cm TL) Thalassoma and Cirrhilabrus that were not targeted by fishing. NTMR protection had no measurable effect on wrasse density, irrespective of species or body size, over 20 (Sumilon) and 31 (Apo) years of protection. However, the density of wrasses was often affected strongly by benthic cover. Hemigymnus spp. had a positive association with hard coral cover, while Thalassoma spp. and Cirrhilabrus spp. had strong positive associations with cover of rubble and dead substratum. These associations were most apparent after environmental disturbances (typhoons, coral bleaching, crown of thorns starfish (COTS) outbreaks, use of explosives and drive nets) reduced live hard coral cover and increased cover of rubble, dead substratum and sand. Disturbances that reduced hard coral cover often reduced the density of Hemigymnus spp. and increased the density of Thalassoma spp. and Cirrhilabrus spp. rapidly (1–2 years). As hard coral recovered, density of Hemigymnus spp. often increased while density of Thalassoma spp. and Cirrhilabrus spp. often decreased, often on scales of 5–10 years. This study demonstrates that wrasse population density was influenced more by changes to benthic cover than by protection from fishing.

Benthic habitat and fish assemblage structure from shallow to mesophotic depths in a storm-impacted marine protected area

Baseline ecological studies of mesophotic coral ecosystems are lacking in the equatorial Indo-West Pacific region where coral reefs are highly threatened by anthropogenic and climate-induced disturbances. Here, we used baited remote underwater video to describe benthic habitat and fish assemblage structure from 10 to 80 m depth at Apo Island, a well-managed marine protected area in the Philippines. We conducted surveys 2 yr after two storms (in 2011 and 2012) caused severe damage to shallow coral communities within the no-take marine reserve (NTMR) of Apo Island, which led to declines in fish populations that had built up over three decades. We found that hard coral cover was restricted to 30 m) was dominated by sand/rubble and rock (dead coral) with low cover of soft corals, sponges and macroalgae. Storm damage appeared to have reached the deepest limit of the fringing reef (40 m) and reduced variability in benthic structure within the NTMR. Species richness and/or abundance of most trophic groups of fish declined with increasing depth regardless of storm damage. There were differences in taxonomic and trophic structure and degree of targeting by fisheries between shallow and mesophotic fish assemblages. Threatened shark species and a fish species previously unreported in the Philippines were recorded at mesophotic depths. Our findings provide a first glimpse of the benthic and fish assemblage structure of Philippine coral reef ecosystems across a wide depth gradient. This work also underscores how a combination of limited coral reef development at mesophotic depths close to shallow reefs and severe habitat loss caused by storms would result in minimal depth refuge for reef fish populations.

TRANSFORMING PROTECTED AREAS INTO EFFECTIVE AND SUSTAINABLE ECOTOURISM DESTINATIONS: LESSONS FROM THE GROUND

A common problem faced by park area managers is the perennial funding crunch, which results to ineffective enforcement of conservation laws and measures. Transforming these protected areas into ecotourism sites is an excellent avenue not only for sustainable community development, but more importantly, as an economic development strategy. This paper is an outcome of the Action Research Project of the Center for Development Management (CDM) of the Asian Institute of Management (AIM) on Protected Area Management. Some NationalIntegrated Protected Areas System (NIPAS) sites showed success in surmounting this funding obstacle by developing the ecotourism potential of their respective locations. This paper draws lessons from the experiences of some selected protected areas including but not limited to the following: the Rajah Sikatuna Park, the Olango Bird and Wildlife Sanctuary, the Puerto Princesa Underground River (PPUR), the Tubbataha Reefs National Park, the Apo Island Seascape and Landscape, etc. It discusses practical considerations on how to utilize ecotourism in promoting appreciation of and support for nature conservation and local culture, while generating economic opportunities for the community.

Decadal-scale effects of benthic habitat and marine reserve protection on Philippine goatfish (F: Mullidae)

Reef fish populations can be affected by both fishing and changes in benthic habitat. Yet, partitioning these effects is often difficult, usually requiring an appropriate sampling design and long-term monitoring. Here we quantify, over a 30-yr period, the effects of benthic habitat change and no-take marine reserve (NTMR) protection on the density and species richness of a lightly harvested benthic-feeding reef fish family, the Mullidae (goatfish), at four Philippine islands. Boosted regression trees demonstrated that goatfish density and species richness had strong negative associations with hard coral cover and strong positive associations with cover of dead substratum. No-take marine reserve protection had no effect on the density or species richness of goatfish over 19 and 30 yr at Sumilon and Apo islands, respectively. However, environmental disturbances (e.g., typhoons, coral bleaching) that reduced hard coral cover subsequently led to increases in goatfish numbers for periods ranging from 2 to 8 yr. After initial increases due to benthic disturbance, goatfish populations decreased during coral recovery, occurring on timescales of 10–20 yr. This long-term, “natural experiment” demonstrated that changes to benthic habitat (bottom-up control) had a far greater effect on Philippine goatfish populations than protection from fishing (a top-down effect) in NTMRs. Given the strong positive response of goatfish populations to loss of live hard coral cover, this group of fishes may be a valuable indicator species for habitat degradation on coral reefs.

Decadal-scale rebuilding of predator biomass in Philippine marine reserves

No-take marine reserves (NTMRs) provide hope that local carrying capacity may be partially restored if reserves are protected long enough. How long is long enough? We assess the duration of protection required for populations of large predatory reef fish in marine reserves to attain new steady states. We monitored biomass of large predatory fish in two marine reserves at Sumilon and Apo Islands, Philippines, almost annually for 26 years (1983-2009), and fit a logistic model to the data. As duration of reserve protection increased, biomass of predatory fish approached an asymptote, although the models suggest that 20-40 years of protection is required to attain new steady states. Thus, for local carrying capacity to be rebuilt, no-take protection must be effective on decadal timescales.

From community-based to centralised national management—A wrong turning for the governance of the marine protected area in Apo Island, Philippines?

Before the mid-1990s, Apo Island, Philippines, was often described as one of the world's best examples of community-based marine management. This paper studies the less-documented transition of the island during the late 1990s from community-based management to centralised national state management. Extensive interviewing of islanders has revealed deep misgivings about the centralised regime—the Protected Area Management Board (PAMB). PAMB's aim of implementing the National Integrated Protected Areas Systems (NIPAS) Act was initially looked upon favourably by islanders, but it has lost that support because of its exclusion of stakeholders from management and its poor institutional performance. The paper's conclusion is that the implementation of the NIPAS Act highlights the limitations of top-down management, and that there is a need to restore an element of local stakeholder participation in the governance of Apo's marine protected area (MPA). A system of co-management between community and national state actors is essential to ensure the long-term sustainability of Apo's marine resources.

A Property Rights Approach to Understanding Human Displacement from Protected Areas: the Case of Marine Protected Areas

The physical, economic, and sociocultural displacement of local peoples from protected areas generates intense discussion among scholars and policy makers. To foster greater precision and clarity in these discussions, we used a conceptual framework from the political economy literature to examine different forms of human displacement from protected areas. Using marine protected areas (MPAs) to ground our analysis, we characterized the 5 types of property rights that are reallocated (lost, secured, and gained) through the establishment of protected areas. All forms of MPA "displacement" involve reallocation of property rights, but the specific types and bundles of rights lost, secured, and gained dramatically shape the magnitude, extent, and equity of MPA impacts--positive and negative--on governance, economic well-being, health, education, social capital, and culture. The impacts of reallocating rights to MPA resources vary within and among social groups, inducing changes in society, in patterns of resource use, and in the environment. To create more environmentally sustainable and socially just conservation practice, a critical next step in conservation social science research is to document and explain variation in the social impacts of protected areas.

No-take Marine Reserves and Reef Fisheries Management in the Philippines: A New People Power Revolution

The marine-conservation and reef fisheries-management program that exists today in the Philippines had humble beginnings in the 1970s at Sumilon and Apo islands. These islands have produced some of the best evidence available that no-take reserves, protected and managed by local communities, can play a key role in biodiversity conservation and fisheries management. Perhaps more importantly, they served as models for an extraordinary expansion of no-take reserves nationally in the Philippines in the past 2 decades. This expansion contributed substantially to a major shift in national policy of management of marine resources. This policy shift partially devolved responsibility from a centralized government bureaucracy to local governments and local communities. Local governments now comanage, along with the national government, marine resources out to 15 km from the coast. Giving some responsibility for management of marine resources to coastal people dependent upon those resources represents, in a very real sense, another "people power revolution" in the Philippines.

DENSITY-DEPENDENT SPILLOVER FROM A MARINE RESERVE: LONG-TERM EVIDENCE

Spillover, the net export of adult fish, is one mechanism by which no-take marine reserves may eventually have a positive influence on adjacent fisheries. Although evidence for spillover has increased recently, mechanisms inducing movement of adult fish from reserve to fished areas are poorly understood. While density-dependent export is a reasonable expectation, given that density of fish targeted by fisheries should increase over time inside well-protected no-take reserves, no study to date has demonstrated development of the process. This study provides evidence consistent with density-dependent export of a planktivorous reef fish, Naso vlamingii, from a small no-take reserve (protected for 20 years) at Apo Island, Philippines. Mean density of N. vlamingii increased threefold inside the reserve between 1983 and 2003. Density approached an asymptote inside the reserve after 15–20 years of protection. Modal size in the reserve increased from 35 to 45 cm total length (TL) over 20 years of protection. In addition, both density and modal size increased outside the reserve close to (200–300 m), but not farther from (300–500 m), the reserve boundary over the 20 years of reserve protection. Movement of adult N. vlamingii across the boundaries of the reserve was rare. Aggressive interactions among adult N. vlamingii were significantly higher (by 3.7 times) inside than outside the reserve. This suggests that density-dependent interactions were more intense inside the reserve. When interacting adults differed in size, the larger individual usually chased away the smaller one. Furthermore, the mean size of adult fish captured by experimental fishing decreased from 35-cm TL 50– 100 m outside the boundary, to 32-cm TL 250–300 m outside the boundary. This represents some of the best evidence available for density-dependent home-range relocation of fish from a no-take reserve.

A long-term, spatially replicated experimental test of the effect of marine reserves on local fish yields

Do no-take marine reserves affect fishery yields? Manipulations of reserve status, and yield estimates, were made at two Philippine islands over two decades. Twenty-five percent and ten percent, respectively, of the coral reefs at Sumilon and Apo islands were made no-take reserves in 1974 and 1982. Biomass of target fish increased inside the no-take reserves 3- to 4.5-fold over 9–18 years. Biomass did not increase outside each reserve. Protection of the Sumilon reserve ceased in 1984. Biomass of targeted fish in the reserve and trap and gillnet catches of these fish declined by 42.7% and 40%, respectively, by 1985. The reserve was reprotected from 1987 to 1991 and from 1995 to 2001. Fish biomass increased in the reserve by 27.2%. Trap and gillnet catches outside the reserve increased 26.9% by 2001. The Apo reserve was protected from 1982 to 2001. Total catch of major fish families was significantly higher after (1985–2001) than before (1981) reserve establishment at Apo, increasing 41.3% between 1981 and 1998–2001. These experiments, plus spillover evidence, suggest that marine reserves may help maintain, or even enhance, local fishery yields in the long-term.

MARINE RESERVE BENEFITS LOCAL FISHERIES

The utility of no‐take marine reserves as fisheries‐management tools is controversial. It is hypothesized that marine reserves will help to sustain fisheries external to them by becoming net exporters of adults (the “spillover effect”) and net exporters of propagules (the “recruitment effect”). Local fishery benefits from spillover will likely generate support from fishing communities for marine reserves. We used underwater visual census to show that biomass of Acanthuridae (surgeonfish) and Carangidae (jacks), two families of reef fish that account for 40–75% of the fishery yield from Apo Island, Philippines, tripled in a well‐protected no‐take reserve over 18 years (1983–2001). Biomass of these families did not change significantly over the same period at a site open to fishing. The reserve protected 10% of the total reef fishing area at the island. Outside the reserve, biomass of these families increased significantly closer to (200–250 m) than farther away from (250–500 m) the reserve boundary over time. We used published estimates of fishery catch and effort, and fisher interviews (creel surveys) to show that the total catch of Carangidae and Acanthuridae combined at Apo Island was significantly higher after (1985–2001) than before (1981) reserve establishment. Hook‐and‐line catch per unit effort (CPUE) at the island was 50% higher during 1998–2001 (reserve protected 16–19 years) than during 1981–1986 (pre‐reserve and early phases of reserve protection). Total hook‐and‐line effort declined by 46% between 1986 and 1998–2001. Hook‐and‐line CPUE of Acanthuridae was significantly higher close to (within 200 m) than far from the reserve. CPUE of Carangidae was significantly higher away from the reserve, possibly reflecting a local oceanographic effect. The benefits of the reserve to local fisheries at the island were higher catch, increased catch rate, and a reduction in fishing effort. The fishery and tourism benefits generated by the reserve have enhanced the living standard of the fishing community.

Marine reserves: long-term protection is required for full recovery of predatory fish populations

No-take marine reserves are advocated widely as a potential solution to the loss of marine biodiversity and ecosystem structure, and to over-fishing. We assess the duration of protection required for unfished populations of large predatory reef fish to attain natural states. We have monitored two marine reserves at Sumilon and Apo Islands, Philippines, regularly for 17 years (1983-2000). The biomass of large predatory fish was still increasing exponentially after 9 and 18 years of protection at Sumilon and Apo reserves, respectively. There was little evidence that the rate of accumulation of biomass inside the reserves was slowing down even after so many years of protection. This suggests that the length of time to full recovery will be considerable. We made two assumptions in order to estimate this period. Firstly, that biomass growth will follow the logistic model. Secondly, the conservative assumption that biomass had already attained 90% of the local carrying capacity of the environments in the reserves. We conclude that the time required for full recovery will be 15 and 40 years at Sumilon and Apo reserves, respectively. Such durations of recovery appear consistent with known life history characteristics of these fish, and with empirical data on recovery rates of heavily exploited fish stocks. By the time the full fisheries or ecosystem benefits from such reserves are apparent, human populations and impacts will have doubled in much of the developing world. Thus, networks of such reserves need to be implemented immediately. Furthermore, the management mechanisms for the reserves need to be successful over timescales of human generations.

Spillover from marine reserves: the case of Naso vlamingii at Apo Island, the Philippines

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 264:15-20 (2003) - doi:10.3354/meps264015 Spillover from marine reserves: the case of Naso vlamingii at Apo Island, the Philippines Garry R. Russ1,*, Angel C. Alcala2, Aileen P. Maypa2 1School of Marine Biology and Aquaculture, James Cook University, Townsville, Queensland 4811, Australia 2Silliman University Angelo King Center for Research and Environmental Management, Silliman University, Dumaguete City 6200, Philippines *Email: garry.russ@jcu.edu.au ABSTRACT: The use of no-take marine reserves as fisheries management tools is controversial. A major expectation of marine reserves is that they will become net exporters of adult biomass (the Œspillover effect¹). Herein, we show that the biomass of the surgeonfish Naso vlamingii tripled over 18 yr (1983 to 2001) in a reserve at Apo Island, Philippines. Over time, the biomass of N. vlamingii increased by a factor of 40 outside but close to the reserve boundaries (200 to 250 m) but not at greater distances (250 to 500 m). In 2000/2001 hook-and-line catch per unit effort (CPUE) for N. vlamingii was 45 times higher within 200 m of the reserve boundary than for all other fishing grounds combined, with 62.5% of the hook-and-line catch records being recorded within 200 m either side of the reserve, in just 11% of the reef fishing area. This comprises some of the best evidence that reserves can benefit fisheries by spillover. KEY WORDS: Marine reserves · Fisheries management · Naso vlamingii · Philippines · Spillover Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 264. Online publication date: December 15, 2003 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2003 Inter-Research.

Recovery of the Apo Island Marine Reserve, Philippines, 2 years after the El Niño bleaching event

Recovery of the Apo Island Marine Reserve, Philippines, 2 years after the El Niño bleaching event

Long-term trends in yield and catch rates of the coral reef fishery at Apo Island, central Philippines

Fish yields and catch rates recorded in the 1980s were compared with daily roving creel surveys carried out in 1997/98, 2000 and 2001 at Apo Island. Total annual fish yields were measured six times over the period 1980–2001. Total fish yield was 19–25 t km–2 year–1, with reef and reef-associated fish accounting for 15–20 t km–2 year–1, for five measurements. A sixth measurement, made in 1986, estimated 36.7 t km–2 year–1. Annual yield remained stable over the study period. Carangidae and Acanthuridae accounted for 26–47% and 16–27% of the catch, respectively. Non-reef catches declined over time, from 6.21 t year–1 in 1980/81 to 1–2 t year–1 in 2000 and 2001. Estimates of annual hook and line catch per unit effort (CPUE) increased from 0.13–0.17 kg man–1 h–1 in 1980/81, to 1–2 kg man–1 h–1 in 1997–2001. For target families, hook and line CPUE was consistently higher in 1997–2001 than in 1980–86. However, hook and line CPUE for Carangidae and Acanthuridae declined significantly between 1997 and 2001. Possible reasons for the long-term patterns of fish yields and catch rates are discussed. Differences in methods used in estimates, and changes in gears and fishing effort over the years, make comparisons difficult.